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[PATCH] usb: typec: tipd: drop double register read in tps6598x_interrupt

Peter Korsgaard posted 1 patch 1 month, 1 week ago 
drivers/usb/typec/tipd/core.c | 2 --
1 file changed, 2 deletions(-)
[PATCH] usb: typec: tipd: drop double register read in tps6598x_interrupt
Posted by Peter Korsgaard 1 month, 1 week ago 
Commit 409c1cfb5a80 ("usb: typec: tipd: fix event checking for tps6598x")
added (by accident?) a double read of the TPS_REG_INT_EVENT1 register.  Drop
that.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
---
 drivers/usb/typec/tipd/core.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/drivers/usb/typec/tipd/core.c b/drivers/usb/typec/tipd/core.c
index 2b1049c9a6f3..2d4fcf62c200 100644
--- a/drivers/usb/typec/tipd/core.c
+++ b/drivers/usb/typec/tipd/core.c
@@ -994,8 +994,6 @@ static irqreturn_t tps6598x_interrupt(int irq, void *data)
 	    TPS_VERSION_HW_VERSION(version) == TPS_VERSION_HW_65987_8_DK)
 		intev_len = TPS_65987_8_INTEVENT_LEN;
 
-	ret = tps6598x_block_read(tps, TPS_REG_INT_EVENT1, event1, intev_len);
-
 	ret = tps6598x_block_read(tps, TPS_REG_INT_EVENT1, event1, intev_len);
 	if (ret) {
 		dev_err(tps->dev, "%s: failed to read event1\n", __func__);
-- 
2.39.5
Re: [PATCH] usb: typec: tipd: drop double register read in tps6598x_interrupt
Posted by Greg KH 1 month, 1 week ago 
On Thu, Nov 06, 2025 at 05:48:49PM +0100, Peter Korsgaard wrote:
> Commit 409c1cfb5a80 ("usb: typec: tipd: fix event checking for tps6598x")
> added (by accident?) a double read of the TPS_REG_INT_EVENT1 register.  Drop
> that.

Are you sure?  Sometimes 2 reads are required.  How was this tested?

thanks,

greg k-h
Re: [PATCH] usb: typec: tipd: drop double register read in tps6598x_interrupt
Posted by Peter Korsgaard 1 month, 1 week ago 
>>>>> "Greg" == Greg KH <gregkh@linuxfoundation.org> writes:

 > On Thu, Nov 06, 2025 at 05:48:49PM +0100, Peter Korsgaard wrote:
 >> Commit 409c1cfb5a80 ("usb: typec: tipd: fix event checking for tps6598x")
 >> added (by accident?) a double read of the TPS_REG_INT_EVENT1 register.  Drop
 >> that.

 > Are you sure?  Sometimes 2 reads are required.  How was this tested?

Hard to be 100% sure, but the code did not have a double read before the
above commit and sticking a printk in the driver like this:

diff --git a/drivers/usb/typec/tipd/core.c b/drivers/usb/typec/tipd/core.c
index 01db27cbf1d1..6687d192dbd4 100644
--- a/drivers/usb/typec/tipd/core.c
+++ b/drivers/usb/typec/tipd/core.c
@@ -536,8 +536,9 @@ static irqreturn_t tps6598x_interrupt(int irq, void *data)
                intev_len = TPS_65987_8_INTEVENT_LEN;

        ret = tps6598x_block_read(tps, TPS_REG_INT_EVENT1, event1, intev_len);
-
+       printk(KERN_ERR "1st: %llx %llx\n", event1[0], event1[1]);
        ret = tps6598x_block_read(tps, TPS_REG_INT_EVENT1, event1, intev_len);
+       printk(KERN_ERR "2nd: %llx %llx\n", event1[0], event1[1]);
        if (ret) {
                dev_err(tps->dev, "%s: failed to read event1\n", __func__);
                goto err_unlock;


and (un)plugging the USB cable I see:

[ 3267.257341] 1st: 3000008 0
[ 3267.262097] 2nd: 3000008 0

[ 3267.345179] 1st: 1000000 0
[ 3267.350512] 2nd: 1000000 0

[ 3267.388947] 1st: 1000000 0
[ 3267.393707] 2nd: 1000000 0

[ 3267.912112] 1st: 1000000 0
[ 3267.916872] 2nd: 1000000 0

[ 3268.049505] 1st: 1000000 0
[ 3268.054773] 2nd: 1000000 0

[ 3269.105173] 1st: 1000000 0
[ 3269.109970] 2nd: 1000000 0

[ 3280.049111] 1st: 3000008 0
[ 3280.053865] 2nd: 3000008 0

So I am fairly sure it is not needed.

-- 
Bye, Peter Korsgaard
Re: [PATCH] usb: typec: tipd: drop double register read in tps6598x_interrupt
Posted by Greg KH 1 month, 1 week ago 
On Fri, Nov 07, 2025 at 04:03:36PM +0100, Peter Korsgaard wrote:
> >>>>> "Greg" == Greg KH <gregkh@linuxfoundation.org> writes:
> 
>  > On Thu, Nov 06, 2025 at 05:48:49PM +0100, Peter Korsgaard wrote:
>  >> Commit 409c1cfb5a80 ("usb: typec: tipd: fix event checking for tps6598x")
>  >> added (by accident?) a double read of the TPS_REG_INT_EVENT1 register.  Drop
>  >> that.
> 
>  > Are you sure?  Sometimes 2 reads are required.  How was this tested?
> 
> Hard to be 100% sure, but the code did not have a double read before the
> above commit and sticking a printk in the driver like this:
> 
> diff --git a/drivers/usb/typec/tipd/core.c b/drivers/usb/typec/tipd/core.c
> index 01db27cbf1d1..6687d192dbd4 100644
> --- a/drivers/usb/typec/tipd/core.c
> +++ b/drivers/usb/typec/tipd/core.c
> @@ -536,8 +536,9 @@ static irqreturn_t tps6598x_interrupt(int irq, void *data)
>                 intev_len = TPS_65987_8_INTEVENT_LEN;
> 
>         ret = tps6598x_block_read(tps, TPS_REG_INT_EVENT1, event1, intev_len);
> -
> +       printk(KERN_ERR "1st: %llx %llx\n", event1[0], event1[1]);
>         ret = tps6598x_block_read(tps, TPS_REG_INT_EVENT1, event1, intev_len);
> +       printk(KERN_ERR "2nd: %llx %llx\n", event1[0], event1[1]);
>         if (ret) {
>                 dev_err(tps->dev, "%s: failed to read event1\n", __func__);
>                 goto err_unlock;
> 
> 
> and (un)plugging the USB cable I see:
> 
> [ 3267.257341] 1st: 3000008 0
> [ 3267.262097] 2nd: 3000008 0
> 
> [ 3267.345179] 1st: 1000000 0
> [ 3267.350512] 2nd: 1000000 0
> 
> [ 3267.388947] 1st: 1000000 0
> [ 3267.393707] 2nd: 1000000 0
> 
> [ 3267.912112] 1st: 1000000 0
> [ 3267.916872] 2nd: 1000000 0
> 
> [ 3268.049505] 1st: 1000000 0
> [ 3268.054773] 2nd: 1000000 0
> 
> [ 3269.105173] 1st: 1000000 0
> [ 3269.109970] 2nd: 1000000 0
> 
> [ 3280.049111] 1st: 3000008 0
> [ 3280.053865] 2nd: 3000008 0
> 
> So I am fairly sure it is not needed.

Sometimes hardware requires it, even if it is not noticed by the actual
read value, so I would like to get an ack from the original author on
this before accepting it.

thanks,

greg k-h
Re: [PATCH] usb: typec: tipd: drop double register read in tps6598x_interrupt
Posted by Heikki Krogerus 1 month, 1 week ago 
Sat, Nov 08, 2025 at 09:43:14AM +0900, Greg KH kirjoitti:
> On Fri, Nov 07, 2025 at 04:03:36PM +0100, Peter Korsgaard wrote:
> > >>>>> "Greg" == Greg KH <gregkh@linuxfoundation.org> writes:
> > 
> >  > On Thu, Nov 06, 2025 at 05:48:49PM +0100, Peter Korsgaard wrote:
> >  >> Commit 409c1cfb5a80 ("usb: typec: tipd: fix event checking for tps6598x")
> >  >> added (by accident?) a double read of the TPS_REG_INT_EVENT1 register.  Drop
> >  >> that.
> > 
> >  > Are you sure?  Sometimes 2 reads are required.  How was this tested?
> > 
> > Hard to be 100% sure, but the code did not have a double read before the
> > above commit and sticking a printk in the driver like this:
> > 
> > diff --git a/drivers/usb/typec/tipd/core.c b/drivers/usb/typec/tipd/core.c
> > index 01db27cbf1d1..6687d192dbd4 100644
> > --- a/drivers/usb/typec/tipd/core.c
> > +++ b/drivers/usb/typec/tipd/core.c
> > @@ -536,8 +536,9 @@ static irqreturn_t tps6598x_interrupt(int irq, void *data)
> >                 intev_len = TPS_65987_8_INTEVENT_LEN;
> > 
> >         ret = tps6598x_block_read(tps, TPS_REG_INT_EVENT1, event1, intev_len);
> > -
> > +       printk(KERN_ERR "1st: %llx %llx\n", event1[0], event1[1]);
> >         ret = tps6598x_block_read(tps, TPS_REG_INT_EVENT1, event1, intev_len);
> > +       printk(KERN_ERR "2nd: %llx %llx\n", event1[0], event1[1]);
> >         if (ret) {
> >                 dev_err(tps->dev, "%s: failed to read event1\n", __func__);
> >                 goto err_unlock;
> > 
> > 
> > and (un)plugging the USB cable I see:
> > 
> > [ 3267.257341] 1st: 3000008 0
> > [ 3267.262097] 2nd: 3000008 0
> > 
> > [ 3267.345179] 1st: 1000000 0
> > [ 3267.350512] 2nd: 1000000 0
> > 
> > [ 3267.388947] 1st: 1000000 0
> > [ 3267.393707] 2nd: 1000000 0
> > 
> > [ 3267.912112] 1st: 1000000 0
> > [ 3267.916872] 2nd: 1000000 0
> > 
> > [ 3268.049505] 1st: 1000000 0
> > [ 3268.054773] 2nd: 1000000 0
> > 
> > [ 3269.105173] 1st: 1000000 0
> > [ 3269.109970] 2nd: 1000000 0
> > 
> > [ 3280.049111] 1st: 3000008 0
> > [ 3280.053865] 2nd: 3000008 0
> > 
> > So I am fairly sure it is not needed.
> 
> Sometimes hardware requires it, even if it is not noticed by the actual
> read value, so I would like to get an ack from the original author on
> this before accepting it.

The hardware should not require it. Javier, can you comment on this?
If there really is need to do double read, then there needs to be a
comment explaining why IMO.

thanks,

-- 
heikki

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