On 2025/8/29 04:44, Rob Herring wrote:
> On Thu, Aug 28, 2025 at 9:00 AM Hans Zhang <18255117159@163.com> wrote:
>>
>> From: Hans Zhang <hans.zhang@cixtech.com>
>>
>> Register bit manipulation in DesignWare PCIe controllers currently
>> uses repetitive read-modify-write sequences across multiple drivers.
>> This pattern leads to code duplication and increases maintenance
>> complexity as each driver implements similar logic with minor variations.
>>
>> This series introduces dw_pcie_*_dword() to centralize atomic
>> register modification. The helper performs read-clear-set-write operations
>> in a single function, replacing open-coded implementations. Subsequent
>> patches refactor individual drivers to use this helper, eliminating
>> redundant code and ensuring consistent bit handling.
>>
>> The change reduces overall code size by ~350 lines while improving
>> maintainability. Each controller driver is updated in a separate
>> patch to preserve bisectability and simplify review.
>
> If RMW functions are an improvement, then they should go in io.h. I
> don't think they are because they obfuscate the exact register
> modifications and the possible need for locking. With common API,
> anyone that understands kernel APIs will know what's going on. With a
> driver specific API, then you have to go lookup what the API does
> exactly. So I don't think this is an improvement.
>
> Rob
Dear Rob,
Thank you very much for your reply.
My initial idea was to simplify the logic we wrote a lot of RMW under
the DWC driver. Then I saw that there were similar well-handled codes in
the linux kernel, so I came to do some cleaning work.
drivers/pci/access.c
int pcie_capability_clear_and_set_dword(struct pci_dev *dev, int pos,
u32 clear, u32 set)
{
int ret;
u32 val;
ret = pcie_capability_read_dword(dev, pos, &val);
if (ret)
return ret;
val &= ~clear;
val |= set;
return pcie_capability_write_dword(dev, pos, val);
}
EXPORT_SYMBOL(pcie_capability_clear_and_set_dword);
include/linux/pci.h
static inline int pcie_capability_set_dword(struct pci_dev *dev, int pos,
u32 set)
{
return pcie_capability_clear_and_set_dword(dev, pos, 0, set);
}
static inline int pcie_capability_clear_dword(struct pci_dev *dev, int pos,
u32 clear)
{
return pcie_capability_clear_and_set_dword(dev, pos, clear, 0);
}
And the subsequent introduced API: Personally, I think they are very
valuable for reference. Of course, it depends on the final opinions of
the maintainer and all of you.
drivers/pci/access.c
void pci_clear_and_set_config_dword(const struct pci_dev *dev, int pos,
u32 clear, u32 set)
{
u32 val;
pci_read_config_dword(dev, pos, &val);
val &= ~clear;
val |= set;
pci_write_config_dword(dev, pos, val);
}
EXPORT_SYMBOL(pci_clear_and_set_config_dword);
Best regards,
Hans