Quoting Doug Anderson (2020-10-29 09:22:55)
> Hi,
>
> On Wed, Oct 28, 2020 at 6:12 PM Stephen Boyd <swboyd@xxxxxxxxxxxx> 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.
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