linux-kernel - Re: [PATCH 08/10] drm: bridge: it66121: Set DDC preamble only once before reading EDID

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Date:   Thu, 15 Dec 2022 12:23:25 +0100
From:   Robert Foss <robert.foss@...aro.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Phong LE <ple@...libre.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Andrzej Hajda <andrzej.hajda@...el.com>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        list@...ndingux.net, dri-devel@...ts.freedesktop.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/10] drm: bridge: it66121: Set DDC preamble only once
 before reading EDID

On Wed, 14 Dec 2022 at 13:59, Paul Cercueil <paul@...pouillou.net> wrote:
>
> The DDC preamble and target address only need to be set once before
> reading the EDID, even if multiple segments have to be read.
>
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
>  drivers/gpu/drm/bridge/ite-it66121.c | 28 ++++++++++++++++------------
>  1 file changed, 16 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/ite-it66121.c b/drivers/gpu/drm/bridge/ite-it66121.c
> index 5335d4abd7c5..7972003d4776 100644
> --- a/drivers/gpu/drm/bridge/ite-it66121.c
> +++ b/drivers/gpu/drm/bridge/ite-it66121.c
> @@ -506,9 +506,6 @@ static int it66121_get_edid_block(void *context, u8 *buf,
>         while (remain > 0) {
>                 cnt = (remain > IT66121_EDID_FIFO_SIZE) ?
>                                 IT66121_EDID_FIFO_SIZE : remain;
> -               ret = it66121_preamble_ddc(ctx);
> -               if (ret)
> -                       return ret;
>
>                 ret = regmap_write(ctx->regmap, IT66121_DDC_COMMAND_REG,
>                                    IT66121_DDC_COMMAND_FIFO_CLR);
> @@ -519,15 +516,6 @@ static int it66121_get_edid_block(void *context, u8 *buf,
>                 if (ret)
>                         return ret;
>
> -               ret = it66121_preamble_ddc(ctx);
> -               if (ret)
> -                       return ret;
> -
> -               ret = regmap_write(ctx->regmap, IT66121_DDC_HEADER_REG,
> -                                  IT66121_DDC_HEADER_EDID);
> -               if (ret)
> -                       return ret;
> -
>                 ret = regmap_write(ctx->regmap, IT66121_DDC_OFFSET_REG, offset);
>                 if (ret)
>                         return ret;
> @@ -842,9 +830,25 @@ static struct edid *it66121_bridge_get_edid(struct drm_bridge *bridge,
>  {
>         struct it66121_ctx *ctx = container_of(bridge, struct it66121_ctx, bridge);
>         struct edid *edid;
> +       int ret;
>
>         mutex_lock(&ctx->lock);
> +       ret = it66121_preamble_ddc(ctx);
> +       if (ret) {
> +               edid = ERR_PTR(ret);
> +               goto out_unlock;
> +       }
> +
> +       ret = regmap_write(ctx->regmap, IT66121_DDC_HEADER_REG,
> +                          IT66121_DDC_HEADER_EDID);
> +       if (ret) {
> +               edid = ERR_PTR(ret);
> +               goto out_unlock;
> +       }
> +
>         edid = drm_do_get_edid(connector, it66121_get_edid_block, ctx);
> +
> +out_unlock:
>         mutex_unlock(&ctx->lock);
>
>         return edid;
> --
> 2.35.1
>

Reviewed-by: Robert Foss <robert.foss@...aro.org>