Re: [PATCH 4/4] drm/bridge: ti-sn65dsi86: Update reply on aux failures

[Stephen Boyd <swboyd@chromium.org>]

Quoting Doug Anderson (2020-10-29 09:22:55)
> Hi,
> 
> On Wed, Oct 28, 2020 at 6:12 PM Stephen Boyd <swboyd@chromium.org> wrote:
> >
> > We should be setting the drm_dp_aux_msg::reply field if a NACK or a
> > SHORT reply happens.
> 
> I don't think you update the "reply" field for SHORT, right?  You just
> return a different size?

Correct.

> 
> 
> > diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> > index 6b6e98ca2881..19737bc01b8f 100644
> > --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> > +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> > @@ -909,10 +910,32 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
> >         ret = regmap_read(pdata->regmap, SN_AUX_CMD_STATUS_REG, &val);
> >         if (ret)
> >                 return ret;
> > -       else if ((val & AUX_IRQ_STATUS_NAT_I2C_FAIL)
> > -                || (val & AUX_IRQ_STATUS_AUX_RPLY_TOUT)
> > -                || (val & AUX_IRQ_STATUS_AUX_SHORT))
> > -               return -ENXIO;
> > +
> > +       if (val & AUX_IRQ_STATUS_AUX_RPLY_TOUT) {
> > +               /*
> > +                * The hardware tried the message seven times per the DP spec
> > +                * but it hit a timeout. We ignore defers here because they're
> > +                * handled in hardware.
> > +                */
> > +               return -ETIMEDOUT;
> > +       }
> > +       if (val & AUX_IRQ_STATUS_AUX_SHORT) {
> > +               ret = regmap_read(pdata->regmap, SN_AUX_LENGTH_REG, &len);
> > +               if (ret)
> > +                       return ret;
> 
> IIUC, your digging through the code showed that in order to fully
> handle the "SHORT" case you also needed to add support for
> "DP_AUX_I2C_WRITE_STATUS_UPDATE", right?

Oh yeah. If a short reply happens and it is aux over i2c then
drm_dp_i2c_msg_write_status_update() is called and
DP_AUX_I2C_WRITE_STATUS_UPDATE is set and then we try a transfer again.
We need to handle that type of request in this ti_sn_aux_transfer()
function.

> 
> Even without handling "DP_AUX_I2C_WRITE_STATUS_UPDATE" though, this
> patch seems to be an improvement and I'd support landing it.
> 
> Oh, I guess one other thing: I think this is all from code inspection,
> right?  You didn't manage to reproduce anything that would tickle one
> of these code paths?  Might be worth mentioning, even if "after the
> cut"?
> 

Yes, just code inspection. I can add that detail to the commit text.