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

[Heikki Krogerus <heikki.krogerus@linux.intel.com>]

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