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

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Date:   Thu, 29 Oct 2020 09:22:55 -0700
From:   Doug Anderson <dianders@...omium.org>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        LKML <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Sean Paul <seanpaul@...omium.org>,
        Sam Ravnborg <sam@...nborg.org>
Subject: Re: [PATCH 4/4] drm/bridge: ti-sn65dsi86: Update reply on aux failures

Hi,

On Wed, Oct 28, 2020 at 6:12 PM Stephen Boyd <swboyd@...omium.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?


> Update the error bit handling logic in
> ti_sn_aux_transfer() to handle these cases and notify upper layers that
> such errors have happened. This helps the retry logic understand that a
> timeout has happened, or to shorten the read length if the panel isn't
> able to handle the longest read possible.
>
> Cc: Douglas Anderson <dianders@...omium.org>
> Cc: Laurent Pinchart <Laurent.pinchart@...asonboard.com>
> Cc: Jonas Karlman <jonas@...boo.se>
> Cc: Jernej Skrabec <jernej.skrabec@...l.net>
> Cc: Sean Paul <seanpaul@...omium.org>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> ---
>  drivers/gpu/drm/bridge/ti-sn65dsi86.c | 31 +++++++++++++++++++++++----
>  1 file changed, 27 insertions(+), 4 deletions(-)
>
> 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
> @@ -878,6 +878,7 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
>         case DP_AUX_NATIVE_READ:
>         case DP_AUX_I2C_READ:
>                 regmap_write(pdata->regmap, SN_AUX_CMD_REG, request_val);
> +               msg->reply = 0; /* Assume it's good */
>                 break;
>         default:
>                 return -EINVAL;
> @@ -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?

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"?

-Doug