Remove obsolete pci_bus_speed2lnkctl2() function and utilize the common
PCIE_SPEED2LNKCTL2_TLS() macro instead.
Signed-off-by: Hans Zhang <18255117159@163.com>
Acked-by: Manivannan Sadhasivam <mani@kernel.org>
---
drivers/pci/pcie/bwctrl.c | 19 +------------------
1 file changed, 1 insertion(+), 18 deletions(-)
diff --git a/drivers/pci/pcie/bwctrl.c b/drivers/pci/pcie/bwctrl.c
index 36f939f23d34..802ab8daf68b 100644
--- a/drivers/pci/pcie/bwctrl.c
+++ b/drivers/pci/pcie/bwctrl.c
@@ -53,23 +53,6 @@ static bool pcie_valid_speed(enum pci_bus_speed speed)
return (speed >= PCIE_SPEED_2_5GT) && (speed <= PCIE_SPEED_64_0GT);
}
-static u16 pci_bus_speed2lnkctl2(enum pci_bus_speed speed)
-{
- static const u8 speed_conv[] = {
- [PCIE_SPEED_2_5GT] = PCI_EXP_LNKCTL2_TLS_2_5GT,
- [PCIE_SPEED_5_0GT] = PCI_EXP_LNKCTL2_TLS_5_0GT,
- [PCIE_SPEED_8_0GT] = PCI_EXP_LNKCTL2_TLS_8_0GT,
- [PCIE_SPEED_16_0GT] = PCI_EXP_LNKCTL2_TLS_16_0GT,
- [PCIE_SPEED_32_0GT] = PCI_EXP_LNKCTL2_TLS_32_0GT,
- [PCIE_SPEED_64_0GT] = PCI_EXP_LNKCTL2_TLS_64_0GT,
- };
-
- if (WARN_ON_ONCE(!pcie_valid_speed(speed)))
- return 0;
-
- return speed_conv[speed];
-}
-
static inline u16 pcie_supported_speeds2target_speed(u8 supported_speeds)
{
return __fls(supported_speeds);
@@ -91,7 +74,7 @@ static u16 pcie_bwctrl_select_speed(struct pci_dev *port, enum pci_bus_speed spe
u8 desired_speeds, supported_speeds;
struct pci_dev *dev;
- desired_speeds = GENMASK(pci_bus_speed2lnkctl2(speed_req),
+ desired_speeds = GENMASK(PCIE_SPEED2LNKCTL2_TLS(speed_req),
__fls(PCI_EXP_LNKCAP2_SLS_2_5GB));
supported_speeds = port->supported_speeds;
--
2.25.1On Sat, Aug 16, 2025 at 11:46:33PM +0800, Hans Zhang wrote:
> Remove obsolete pci_bus_speed2lnkctl2() function and utilize the common
> PCIE_SPEED2LNKCTL2_TLS() macro instead.
[...]
> +++ b/drivers/pci/pcie/bwctrl.c
> @@ -53,23 +53,6 @@ static bool pcie_valid_speed(enum pci_bus_speed speed)
> return (speed >= PCIE_SPEED_2_5GT) && (speed <= PCIE_SPEED_64_0GT);
> }
>
> -static u16 pci_bus_speed2lnkctl2(enum pci_bus_speed speed)
> -{
> - static const u8 speed_conv[] = {
> - [PCIE_SPEED_2_5GT] = PCI_EXP_LNKCTL2_TLS_2_5GT,
> - [PCIE_SPEED_5_0GT] = PCI_EXP_LNKCTL2_TLS_5_0GT,
> - [PCIE_SPEED_8_0GT] = PCI_EXP_LNKCTL2_TLS_8_0GT,
> - [PCIE_SPEED_16_0GT] = PCI_EXP_LNKCTL2_TLS_16_0GT,
> - [PCIE_SPEED_32_0GT] = PCI_EXP_LNKCTL2_TLS_32_0GT,
> - [PCIE_SPEED_64_0GT] = PCI_EXP_LNKCTL2_TLS_64_0GT,
> - };
> -
> - if (WARN_ON_ONCE(!pcie_valid_speed(speed)))
> - return 0;
> -
> - return speed_conv[speed];
> -}
> -
> static inline u16 pcie_supported_speeds2target_speed(u8 supported_speeds)
> {
> return __fls(supported_speeds);
> @@ -91,7 +74,7 @@ static u16 pcie_bwctrl_select_speed(struct pci_dev *port, enum pci_bus_speed spe
> u8 desired_speeds, supported_speeds;
> struct pci_dev *dev;
>
> - desired_speeds = GENMASK(pci_bus_speed2lnkctl2(speed_req),
> + desired_speeds = GENMASK(PCIE_SPEED2LNKCTL2_TLS(speed_req),
> __fls(PCI_EXP_LNKCAP2_SLS_2_5GB));
No, that's not good. The function you're removing above,
pci_bus_speed2lnkctl2(), uses an array to look up the speed.
That's an O(1) operation, it doesn't get any more efficient
than that. It was a deliberate design decision to do this
when the bandwidth controller was created.
Whereas the function you're using instead uses a series
of ternary operators. That's no longer an O(1) operation,
the compiler translates it into a series of conditional
branches, so essentially an O(n) lookup (where n is the
number of speeds). So it's less efficient and less elegant.
Please come up with an approach that doesn't make this
worse than before.
Thanks,
Lukas
On 2025/8/17 04:13, Lukas Wunner wrote:
> On Sat, Aug 16, 2025 at 11:46:33PM +0800, Hans Zhang wrote:
>> Remove obsolete pci_bus_speed2lnkctl2() function and utilize the common
>> PCIE_SPEED2LNKCTL2_TLS() macro instead.
> [...]
>> +++ b/drivers/pci/pcie/bwctrl.c
>> @@ -53,23 +53,6 @@ static bool pcie_valid_speed(enum pci_bus_speed speed)
>> return (speed >= PCIE_SPEED_2_5GT) && (speed <= PCIE_SPEED_64_0GT);
>> }
>>
>> -static u16 pci_bus_speed2lnkctl2(enum pci_bus_speed speed)
>> -{
>> - static const u8 speed_conv[] = {
>> - [PCIE_SPEED_2_5GT] = PCI_EXP_LNKCTL2_TLS_2_5GT,
>> - [PCIE_SPEED_5_0GT] = PCI_EXP_LNKCTL2_TLS_5_0GT,
>> - [PCIE_SPEED_8_0GT] = PCI_EXP_LNKCTL2_TLS_8_0GT,
>> - [PCIE_SPEED_16_0GT] = PCI_EXP_LNKCTL2_TLS_16_0GT,
>> - [PCIE_SPEED_32_0GT] = PCI_EXP_LNKCTL2_TLS_32_0GT,
>> - [PCIE_SPEED_64_0GT] = PCI_EXP_LNKCTL2_TLS_64_0GT,
>> - };
>> -
>> - if (WARN_ON_ONCE(!pcie_valid_speed(speed)))
>> - return 0;
>> -
>> - return speed_conv[speed];
>> -}
>> -
>> static inline u16 pcie_supported_speeds2target_speed(u8 supported_speeds)
>> {
>> return __fls(supported_speeds);
>> @@ -91,7 +74,7 @@ static u16 pcie_bwctrl_select_speed(struct pci_dev *port, enum pci_bus_speed spe
>> u8 desired_speeds, supported_speeds;
>> struct pci_dev *dev;
>>
>> - desired_speeds = GENMASK(pci_bus_speed2lnkctl2(speed_req),
>> + desired_speeds = GENMASK(PCIE_SPEED2LNKCTL2_TLS(speed_req),
>> __fls(PCI_EXP_LNKCAP2_SLS_2_5GB));
>
> No, that's not good. The function you're removing above,
> pci_bus_speed2lnkctl2(), uses an array to look up the speed.
> That's an O(1) operation, it doesn't get any more efficient
> than that. It was a deliberate design decision to do this
> when the bandwidth controller was created.
>
> Whereas the function you're using instead uses a series
> of ternary operators. That's no longer an O(1) operation,
> the compiler translates it into a series of conditional
> branches, so essentially an O(n) lookup (where n is the
> number of speeds). So it's less efficient and less elegant.
>
> Please come up with an approach that doesn't make this
> worse than before.
Dear Lukas,
Thank you very much for your reply.
I think the original static array will waste some memory space.
Originally, we only needed a size of 6 bytes, but in reality, the size
of this array is 26 bytes.
static const u8 speed_conv[] = {
[PCIE_SPEED_2_5GT] = PCI_EXP_LNKCTL2_TLS_2_5GT,
[PCIE_SPEED_5_0GT] = PCI_EXP_LNKCTL2_TLS_5_0GT,
[PCIE_SPEED_8_0GT] = PCI_EXP_LNKCTL2_TLS_8_0GT,
[PCIE_SPEED_16_0GT] = PCI_EXP_LNKCTL2_TLS_16_0GT,
[PCIE_SPEED_32_0GT] = PCI_EXP_LNKCTL2_TLS_32_0GT,
[PCIE_SPEED_64_0GT] = PCI_EXP_LNKCTL2_TLS_64_0GT,
};
What do you think if the first patch is modified as follows?
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 34f65d69662e..d6c3333315a0 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -422,6 +422,28 @@ void pci_bus_put(struct pci_bus *bus);
PCI_SPEED_UNKNOWN); \
})
+static inline u16 pcie_speed_to_lnkctl2_tls(enum pci_bus_speed speed)
+{
+ /*
+ * Convert PCIe speed enum to LNKCTL2_TLS value using
+ * direct arithmetic:
+ *
+ * Speed enum: 0x14 (2.5GT) -> TLS = 0x1
+ * 0x15 (5.0GT) -> TLS = 0x2
+ * 0x16 (8.0GT) -> TLS = 0x3
+ * 0x17 (16.0GT)-> TLS = 0x4
+ * 0x18 (32.0GT)-> TLS = 0x5
+ * 0x19 (64.0GT)-> TLS = 0x6
+ *
+ * Formula: TLS = (speed - PCIE_SPEED_2_5GT) + 1
+ */
+ if (!WARN_ON_ONCE(speed >= PCIE_SPEED_2_5GT ||
+ speed <= PCIE_SPEED_64_0GT))
+ return 0;
+
+ return (speed - PCIE_SPEED_2_5GT) + PCI_EXP_LNKCTL2_TLS_2_5GT;
+}
+
/* PCIe speed to Mb/s reduced by encoding overhead */
#define PCIE_SPEED2MBS_ENC(speed) \
((speed) == PCIE_SPEED_64_0GT ? 64000*1/1 : \
If you think the above plan is feasible. Then, should all the following
macro definitions be changed to inline functions?
drivers/pci/pci.h
#define PCIE_LNKCAP_SLS2SPEED(lnkcap) \
({ \
u32 lnkcap_sls = (lnkcap) & PCI_EXP_LNKCAP_SLS; \
\
(lnkcap_sls == PCI_EXP_LNKCAP_SLS_64_0GB ? PCIE_SPEED_64_0GT : \
lnkcap_sls == PCI_EXP_LNKCAP_SLS_32_0GB ? PCIE_SPEED_32_0GT : \
lnkcap_sls == PCI_EXP_LNKCAP_SLS_16_0GB ? PCIE_SPEED_16_0GT : \
lnkcap_sls == PCI_EXP_LNKCAP_SLS_8_0GB ? PCIE_SPEED_8_0GT : \
lnkcap_sls == PCI_EXP_LNKCAP_SLS_5_0GB ? PCIE_SPEED_5_0GT : \
lnkcap_sls == PCI_EXP_LNKCAP_SLS_2_5GB ? PCIE_SPEED_2_5GT : \
PCI_SPEED_UNKNOWN); \
})
/* PCIe link information from Link Capabilities 2 */
#define PCIE_LNKCAP2_SLS2SPEED(lnkcap2) \
((lnkcap2) & PCI_EXP_LNKCAP2_SLS_64_0GB ? PCIE_SPEED_64_0GT : \
(lnkcap2) & PCI_EXP_LNKCAP2_SLS_32_0GB ? PCIE_SPEED_32_0GT : \
(lnkcap2) & PCI_EXP_LNKCAP2_SLS_16_0GB ? PCIE_SPEED_16_0GT : \
(lnkcap2) & PCI_EXP_LNKCAP2_SLS_8_0GB ? PCIE_SPEED_8_0GT : \
(lnkcap2) & PCI_EXP_LNKCAP2_SLS_5_0GB ? PCIE_SPEED_5_0GT : \
(lnkcap2) & PCI_EXP_LNKCAP2_SLS_2_5GB ? PCIE_SPEED_2_5GT : \
PCI_SPEED_UNKNOWN)
#define PCIE_LNKCTL2_TLS2SPEED(lnkctl2) \
({ \
u16 lnkctl2_tls = (lnkctl2) & PCI_EXP_LNKCTL2_TLS; \
\
(lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_64_0GT ? PCIE_SPEED_64_0GT : \
lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_32_0GT ? PCIE_SPEED_32_0GT : \
lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_16_0GT ? PCIE_SPEED_16_0GT : \
lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_8_0GT ? PCIE_SPEED_8_0GT : \
lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_5_0GT ? PCIE_SPEED_5_0GT : \
lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_2_5GT ? PCIE_SPEED_2_5GT : \
PCI_SPEED_UNKNOWN); \
})
Best regards,
Hans
On Sun, Aug 17, 2025 at 11:02:10PM GMT, Hans Zhang wrote:
>
>
> On 2025/8/17 04:13, Lukas Wunner wrote:
> > On Sat, Aug 16, 2025 at 11:46:33PM +0800, Hans Zhang wrote:
> > > Remove obsolete pci_bus_speed2lnkctl2() function and utilize the common
> > > PCIE_SPEED2LNKCTL2_TLS() macro instead.
> > [...]
> > > +++ b/drivers/pci/pcie/bwctrl.c
> > > @@ -53,23 +53,6 @@ static bool pcie_valid_speed(enum pci_bus_speed speed)
> > > return (speed >= PCIE_SPEED_2_5GT) && (speed <= PCIE_SPEED_64_0GT);
> > > }
> > > -static u16 pci_bus_speed2lnkctl2(enum pci_bus_speed speed)
> > > -{
> > > - static const u8 speed_conv[] = {
> > > - [PCIE_SPEED_2_5GT] = PCI_EXP_LNKCTL2_TLS_2_5GT,
> > > - [PCIE_SPEED_5_0GT] = PCI_EXP_LNKCTL2_TLS_5_0GT,
> > > - [PCIE_SPEED_8_0GT] = PCI_EXP_LNKCTL2_TLS_8_0GT,
> > > - [PCIE_SPEED_16_0GT] = PCI_EXP_LNKCTL2_TLS_16_0GT,
> > > - [PCIE_SPEED_32_0GT] = PCI_EXP_LNKCTL2_TLS_32_0GT,
> > > - [PCIE_SPEED_64_0GT] = PCI_EXP_LNKCTL2_TLS_64_0GT,
> > > - };
> > > -
> > > - if (WARN_ON_ONCE(!pcie_valid_speed(speed)))
> > > - return 0;
> > > -
> > > - return speed_conv[speed];
> > > -}
> > > -
> > > static inline u16 pcie_supported_speeds2target_speed(u8 supported_speeds)
> > > {
> > > return __fls(supported_speeds);
> > > @@ -91,7 +74,7 @@ static u16 pcie_bwctrl_select_speed(struct pci_dev *port, enum pci_bus_speed spe
> > > u8 desired_speeds, supported_speeds;
> > > struct pci_dev *dev;
> > > - desired_speeds = GENMASK(pci_bus_speed2lnkctl2(speed_req),
> > > + desired_speeds = GENMASK(PCIE_SPEED2LNKCTL2_TLS(speed_req),
> > > __fls(PCI_EXP_LNKCAP2_SLS_2_5GB));
> >
> > No, that's not good. The function you're removing above,
> > pci_bus_speed2lnkctl2(), uses an array to look up the speed.
> > That's an O(1) operation, it doesn't get any more efficient
> > than that. It was a deliberate design decision to do this
> > when the bandwidth controller was created.
> >
> > Whereas the function you're using instead uses a series
> > of ternary operators. That's no longer an O(1) operation,
> > the compiler translates it into a series of conditional
> > branches, so essentially an O(n) lookup (where n is the
> > number of speeds). So it's less efficient and less elegant.
> >
> > Please come up with an approach that doesn't make this
> > worse than before.
>
>
> Dear Lukas,
>
> Thank you very much for your reply.
>
> I think the original static array will waste some memory space. Originally,
> we only needed a size of 6 bytes, but in reality, the size of this array is
> 26 bytes.
>
This is just one time allocation as the array is a 'static const', which is not
a big deal.
> static const u8 speed_conv[] = {
> [PCIE_SPEED_2_5GT] = PCI_EXP_LNKCTL2_TLS_2_5GT,
> [PCIE_SPEED_5_0GT] = PCI_EXP_LNKCTL2_TLS_5_0GT,
> [PCIE_SPEED_8_0GT] = PCI_EXP_LNKCTL2_TLS_8_0GT,
> [PCIE_SPEED_16_0GT] = PCI_EXP_LNKCTL2_TLS_16_0GT,
> [PCIE_SPEED_32_0GT] = PCI_EXP_LNKCTL2_TLS_32_0GT,
> [PCIE_SPEED_64_0GT] = PCI_EXP_LNKCTL2_TLS_64_0GT,
> };
[...]
> drivers/pci/pci.h
> #define PCIE_LNKCAP_SLS2SPEED(lnkcap) \
> ({ \
> u32 lnkcap_sls = (lnkcap) & PCI_EXP_LNKCAP_SLS; \
> \
> (lnkcap_sls == PCI_EXP_LNKCAP_SLS_64_0GB ? PCIE_SPEED_64_0GT : \
> lnkcap_sls == PCI_EXP_LNKCAP_SLS_32_0GB ? PCIE_SPEED_32_0GT : \
> lnkcap_sls == PCI_EXP_LNKCAP_SLS_16_0GB ? PCIE_SPEED_16_0GT : \
> lnkcap_sls == PCI_EXP_LNKCAP_SLS_8_0GB ? PCIE_SPEED_8_0GT : \
> lnkcap_sls == PCI_EXP_LNKCAP_SLS_5_0GB ? PCIE_SPEED_5_0GT : \
> lnkcap_sls == PCI_EXP_LNKCAP_SLS_2_5GB ? PCIE_SPEED_2_5GT : \
> PCI_SPEED_UNKNOWN); \
> })
>
> /* PCIe link information from Link Capabilities 2 */
> #define PCIE_LNKCAP2_SLS2SPEED(lnkcap2) \
> ((lnkcap2) & PCI_EXP_LNKCAP2_SLS_64_0GB ? PCIE_SPEED_64_0GT : \
> (lnkcap2) & PCI_EXP_LNKCAP2_SLS_32_0GB ? PCIE_SPEED_32_0GT : \
> (lnkcap2) & PCI_EXP_LNKCAP2_SLS_16_0GB ? PCIE_SPEED_16_0GT : \
> (lnkcap2) & PCI_EXP_LNKCAP2_SLS_8_0GB ? PCIE_SPEED_8_0GT : \
> (lnkcap2) & PCI_EXP_LNKCAP2_SLS_5_0GB ? PCIE_SPEED_5_0GT : \
> (lnkcap2) & PCI_EXP_LNKCAP2_SLS_2_5GB ? PCIE_SPEED_2_5GT : \
> PCI_SPEED_UNKNOWN)
>
> #define PCIE_LNKCTL2_TLS2SPEED(lnkctl2) \
> ({ \
> u16 lnkctl2_tls = (lnkctl2) & PCI_EXP_LNKCTL2_TLS; \
> \
> (lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_64_0GT ? PCIE_SPEED_64_0GT : \
> lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_32_0GT ? PCIE_SPEED_32_0GT : \
> lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_16_0GT ? PCIE_SPEED_16_0GT : \
> lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_8_0GT ? PCIE_SPEED_8_0GT : \
> lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_5_0GT ? PCIE_SPEED_5_0GT : \
> lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_2_5GT ? PCIE_SPEED_2_5GT : \
> PCI_SPEED_UNKNOWN); \
> })
No, these macros are terrible. They generate more assembly code than needed for
a simple array based lookup. So in the end, they increase the binary size and
also doesn't provide any improvement other than the unification in the textual
form.
I have to take my Acked-by back as I sort of overlooked these factors. As Lukas
rightly said, the pci_bus_speed2lnkctl2() does lookup in O(1), which is what we
want here.
Code refactoring shouldn't come at the expense of the runtime overhead.
- Mani
--
மணிவண்ணன் சதாசிவம்
On 2025/8/18 13:21, Manivannan Sadhasivam wrote:
> EXTERNAL EMAIL
>
> On Sun, Aug 17, 2025 at 11:02:10PM GMT, Hans Zhang wrote:
>>
>>
>> On 2025/8/17 04:13, Lukas Wunner wrote:
>>> On Sat, Aug 16, 2025 at 11:46:33PM +0800, Hans Zhang wrote:
>>>> Remove obsolete pci_bus_speed2lnkctl2() function and utilize the common
>>>> PCIE_SPEED2LNKCTL2_TLS() macro instead.
>>> [...]
>>>> +++ b/drivers/pci/pcie/bwctrl.c
>>>> @@ -53,23 +53,6 @@ static bool pcie_valid_speed(enum pci_bus_speed speed)
>>>> return (speed >= PCIE_SPEED_2_5GT) && (speed <= PCIE_SPEED_64_0GT);
>>>> }
>>>> -static u16 pci_bus_speed2lnkctl2(enum pci_bus_speed speed)
>>>> -{
>>>> - static const u8 speed_conv[] = {
>>>> - [PCIE_SPEED_2_5GT] = PCI_EXP_LNKCTL2_TLS_2_5GT,
>>>> - [PCIE_SPEED_5_0GT] = PCI_EXP_LNKCTL2_TLS_5_0GT,
>>>> - [PCIE_SPEED_8_0GT] = PCI_EXP_LNKCTL2_TLS_8_0GT,
>>>> - [PCIE_SPEED_16_0GT] = PCI_EXP_LNKCTL2_TLS_16_0GT,
>>>> - [PCIE_SPEED_32_0GT] = PCI_EXP_LNKCTL2_TLS_32_0GT,
>>>> - [PCIE_SPEED_64_0GT] = PCI_EXP_LNKCTL2_TLS_64_0GT,
>>>> - };
>>>> -
>>>> - if (WARN_ON_ONCE(!pcie_valid_speed(speed)))
>>>> - return 0;
>>>> -
>>>> - return speed_conv[speed];
>>>> -}
>>>> -
>>>> static inline u16 pcie_supported_speeds2target_speed(u8 supported_speeds)
>>>> {
>>>> return __fls(supported_speeds);
>>>> @@ -91,7 +74,7 @@ static u16 pcie_bwctrl_select_speed(struct pci_dev *port, enum pci_bus_speed spe
>>>> u8 desired_speeds, supported_speeds;
>>>> struct pci_dev *dev;
>>>> - desired_speeds = GENMASK(pci_bus_speed2lnkctl2(speed_req),
>>>> + desired_speeds = GENMASK(PCIE_SPEED2LNKCTL2_TLS(speed_req),
>>>> __fls(PCI_EXP_LNKCAP2_SLS_2_5GB));
>>>
>>> No, that's not good. The function you're removing above,
>>> pci_bus_speed2lnkctl2(), uses an array to look up the speed.
>>> That's an O(1) operation, it doesn't get any more efficient
>>> than that. It was a deliberate design decision to do this
>>> when the bandwidth controller was created.
>>>
>>> Whereas the function you're using instead uses a series
>>> of ternary operators. That's no longer an O(1) operation,
>>> the compiler translates it into a series of conditional
>>> branches, so essentially an O(n) lookup (where n is the
>>> number of speeds). So it's less efficient and less elegant.
>>>
>>> Please come up with an approach that doesn't make this
>>> worse than before.
>>
>>
>> Dear Lukas,
>>
>> Thank you very much for your reply.
>>
>> I think the original static array will waste some memory space. Originally,
>> we only needed a size of 6 bytes, but in reality, the size of this array is
>> 26 bytes.
>>
>
> This is just one time allocation as the array is a 'static const', which is not
> a big deal.
>
>> static const u8 speed_conv[] = {
>> [PCIE_SPEED_2_5GT] = PCI_EXP_LNKCTL2_TLS_2_5GT,
>> [PCIE_SPEED_5_0GT] = PCI_EXP_LNKCTL2_TLS_5_0GT,
>> [PCIE_SPEED_8_0GT] = PCI_EXP_LNKCTL2_TLS_8_0GT,
>> [PCIE_SPEED_16_0GT] = PCI_EXP_LNKCTL2_TLS_16_0GT,
>> [PCIE_SPEED_32_0GT] = PCI_EXP_LNKCTL2_TLS_32_0GT,
>> [PCIE_SPEED_64_0GT] = PCI_EXP_LNKCTL2_TLS_64_0GT,
>> };
>
> [...]
>
>> drivers/pci/pci.h
>> #define PCIE_LNKCAP_SLS2SPEED(lnkcap) \
>> ({ \
>> u32 lnkcap_sls = (lnkcap) & PCI_EXP_LNKCAP_SLS; \
>> \
>> (lnkcap_sls == PCI_EXP_LNKCAP_SLS_64_0GB ? PCIE_SPEED_64_0GT : \
>> lnkcap_sls == PCI_EXP_LNKCAP_SLS_32_0GB ? PCIE_SPEED_32_0GT : \
>> lnkcap_sls == PCI_EXP_LNKCAP_SLS_16_0GB ? PCIE_SPEED_16_0GT : \
>> lnkcap_sls == PCI_EXP_LNKCAP_SLS_8_0GB ? PCIE_SPEED_8_0GT : \
>> lnkcap_sls == PCI_EXP_LNKCAP_SLS_5_0GB ? PCIE_SPEED_5_0GT : \
>> lnkcap_sls == PCI_EXP_LNKCAP_SLS_2_5GB ? PCIE_SPEED_2_5GT : \
>> PCI_SPEED_UNKNOWN); \
>> })
>>
>> /* PCIe link information from Link Capabilities 2 */
>> #define PCIE_LNKCAP2_SLS2SPEED(lnkcap2) \
>> ((lnkcap2) & PCI_EXP_LNKCAP2_SLS_64_0GB ? PCIE_SPEED_64_0GT : \
>> (lnkcap2) & PCI_EXP_LNKCAP2_SLS_32_0GB ? PCIE_SPEED_32_0GT : \
>> (lnkcap2) & PCI_EXP_LNKCAP2_SLS_16_0GB ? PCIE_SPEED_16_0GT : \
>> (lnkcap2) & PCI_EXP_LNKCAP2_SLS_8_0GB ? PCIE_SPEED_8_0GT : \
>> (lnkcap2) & PCI_EXP_LNKCAP2_SLS_5_0GB ? PCIE_SPEED_5_0GT : \
>> (lnkcap2) & PCI_EXP_LNKCAP2_SLS_2_5GB ? PCIE_SPEED_2_5GT : \
>> PCI_SPEED_UNKNOWN)
>>
>> #define PCIE_LNKCTL2_TLS2SPEED(lnkctl2) \
>> ({ \
>> u16 lnkctl2_tls = (lnkctl2) & PCI_EXP_LNKCTL2_TLS; \
>> \
>> (lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_64_0GT ? PCIE_SPEED_64_0GT : \
>> lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_32_0GT ? PCIE_SPEED_32_0GT : \
>> lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_16_0GT ? PCIE_SPEED_16_0GT : \
>> lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_8_0GT ? PCIE_SPEED_8_0GT : \
>> lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_5_0GT ? PCIE_SPEED_5_0GT : \
>> lnkctl2_tls == PCI_EXP_LNKCTL2_TLS_2_5GT ? PCIE_SPEED_2_5GT : \
>> PCI_SPEED_UNKNOWN); \
>> })
>
> No, these macros are terrible. They generate more assembly code than needed for
> a simple array based lookup. So in the end, they increase the binary size and
> also doesn't provide any improvement other than the unification in the textual
> form.
>
> I have to take my Acked-by back as I sort of overlooked these factors. As Lukas
> rightly said, the pci_bus_speed2lnkctl2() does lookup in O(1), which is what we
> want here.
>
> Code refactoring shouldn't come at the expense of the runtime overhead.
>
Dear Mani,
Thank you very much for your reply.
Could you please share your views on modifying PCIE_SPEED2LNKCTL2_TLS to
the pcie_speed_to_lnkctl2_tls inline function? Or simply put the
pci_bus_speed2lnkctl2 in bwctrl.c into drivers/pci/pci.h?
Previous version modifications:
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 12215ee72afb..b5a3ce6c239b 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -419,6 +419,15 @@ void pci_bus_put(struct pci_bus *bus);
(lnkctl2) == PCI_EXP_LNKCTL2_TLS_2_5GT ? PCIE_SPEED_2_5GT : \
PCI_SPEED_UNKNOWN)
+#define PCIE_SPEED2LNKCTL2_TLS(speed) \
+ ((speed) == PCIE_SPEED_2_5GT ? PCI_EXP_LNKCTL2_TLS_2_5GT : \
+ (speed) == PCIE_SPEED_5_0GT ? PCI_EXP_LNKCTL2_TLS_5_0GT : \
+ (speed) == PCIE_SPEED_8_0GT ? PCI_EXP_LNKCTL2_TLS_8_0GT : \
+ (speed) == PCIE_SPEED_16_0GT ? PCI_EXP_LNKCTL2_TLS_16_0GT : \
+ (speed) == PCIE_SPEED_32_0GT ? PCI_EXP_LNKCTL2_TLS_32_0GT : \
+ (speed) == PCIE_SPEED_64_0GT ? PCI_EXP_LNKCTL2_TLS_64_0GT : \
+ 0)
+
/* PCIe speed to Mb/s reduced by encoding overhead */
#define PCIE_SPEED2MBS_ENC(speed) \
((speed) == PCIE_SPEED_64_0GT ? 64000*1/1 : \
Current modifications:
diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 34f65d69662e..d6c3333315a0 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -422,6 +422,28 @@ void pci_bus_put(struct pci_bus *bus);
PCI_SPEED_UNKNOWN); \
})
+static inline u16 pcie_speed_to_lnkctl2_tls(enum pci_bus_speed speed)
+{
+ /*
+ * Convert PCIe speed enum to LNKCTL2_TLS value using
+ * direct arithmetic:
+ *
+ * Speed enum: 0x14 (2.5GT) -> TLS = 0x1
+ * 0x15 (5.0GT) -> TLS = 0x2
+ * 0x16 (8.0GT) -> TLS = 0x3
+ * 0x17 (16.0GT)-> TLS = 0x4
+ * 0x18 (32.0GT)-> TLS = 0x5
+ * 0x19 (64.0GT)-> TLS = 0x6
+ *
+ * Formula: TLS = (speed - PCIE_SPEED_2_5GT) + 1
+ */
+ if (!WARN_ON_ONCE(speed >= PCIE_SPEED_2_5GT ||
+ speed <= PCIE_SPEED_64_0GT))
+ return 0;
+
+ return (speed - PCIE_SPEED_2_5GT) + PCI_EXP_LNKCTL2_TLS_2_5GT;
+}
+
/* PCIe speed to Mb/s reduced by encoding overhead */
#define PCIE_SPEED2MBS_ENC(speed) \
((speed) == PCIE_SPEED_64_0GT ? 64000*1/1 : \
In the future, I will try to find a good way to modify these macro
definitions.
Best regards,
Hans
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