linux-kernel - Re: [PATCH v2] drm/bridge: Clear the DP_AUX_I2C

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Date:   Tue, 1 Mar 2022 16:57:45 +0800
From:   Hsin-Yi Wang <hsinyi@...omium.org>
To:     Xin Ji <xji@...logixsemi.com>
Cc:     Robert Foss <robert.foss@...aro.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Daniel Vetter <daniel@...ll.ch>,
        Andrzej Hajda <andrzej.hajda@...el.com>
Subject: Re: [PATCH v2] drm/bridge: Clear the DP_AUX_I2C_MOT bit passed in aux
 read command.

On Thu, Feb 17, 2022 at 4:31 PM Xin Ji <xji@...logixsemi.com> wrote:
>
> On Thu, Feb 17, 2022 at 04:22:25PM +0800, Hsin-Yi Wang wrote:
> > If the previous transfer didn't end with a command without DP_AUX_I2C_MOT,
> > the next read trasnfer will miss the first byte. But if the command in
> > previous transfer is requested with length 0, it's a no-op to anx7625
> > since it can't process this command. anx7625 requires the last command
> > to be read command with length > 0.
> >
> > It's observed that if we clear the DP_AUX_I2C_MOT in read transfer, we
> > can still get correct data. Clear the read commands with DP_AUX_I2C_MOT
> > bit to fix this issue.
>
> Hi Hsin-Yi, thanks for the patch!
>
> Reviewed-by: Xin Ji <xji@...logixsemi.com>
>
> Thanks,
> Xin

Hi Robert,

Kindly ping on this fix. Thanks.

> >
> > Fixes: adca62ec370c ("drm/bridge: anx7625: Support reading edid through aux channel")
> > Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
> > ---
> > v1->v2: Offline discussed with Xin Ji, it's better to clear the bit on
> > read commands only.
> > ---
> >  drivers/gpu/drm/bridge/analogix/anx7625.c | 2 ++
> >  1 file changed, 2 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/bridge/analogix/anx7625.c b/drivers/gpu/drm/bridge/analogix/anx7625.c
> > index 633618bafd75d3..2805e9bed2c2f4 100644
> > --- a/drivers/gpu/drm/bridge/analogix/anx7625.c
> > +++ b/drivers/gpu/drm/bridge/analogix/anx7625.c
> > @@ -253,6 +253,8 @@ static int anx7625_aux_trans(struct anx7625_data *ctx, u8 op, u32 address,
> >       addrm = (address >> 8) & 0xFF;
> >       addrh = (address >> 16) & 0xFF;
> >
> > +     if (!is_write)
> > +             op &= ~DP_AUX_I2C_MOT;
> >       cmd = DPCD_CMD(len, op);
> >
> >       /* Set command and length */
> > --
> > 2.35.1.265.g69c8d7142f-goog