linux-kernel - Re: [PATCH 05/10] drm: bridge: it66121: Fix wait for DDC ready

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Date:   Thu, 15 Dec 2022 12:14:19 +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 05/10] drm: bridge: it66121: Fix wait for DDC ready

On Wed, 14 Dec 2022 at 13:59, Paul Cercueil <paul@...pouillou.net> wrote:
>
> The function it66121_wait_ddc_ready() would previously read the status
> register until "true", which means it never actually polled anything and
> would just read the register once.
>
> Now, it will properly wait until the DDC hardware is ready or until it
> reported an error.
>
> The 'busy' variable was also renamed to 'error' since these bits are set
> on error and not when the DDC hardware is busy.
>
> Since the DDC ready function is now working properly, the msleep(20) can
> be removed.
>
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
>  drivers/gpu/drm/bridge/ite-it66121.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/ite-it66121.c b/drivers/gpu/drm/bridge/ite-it66121.c
> index 0a4fdfd7af44..bfb9c87a7019 100644
> --- a/drivers/gpu/drm/bridge/ite-it66121.c
> +++ b/drivers/gpu/drm/bridge/ite-it66121.c
> @@ -440,15 +440,17 @@ static int it66121_configure_afe(struct it66121_ctx *ctx,
>  static inline int it66121_wait_ddc_ready(struct it66121_ctx *ctx)
>  {
>         int ret, val;
> -       u32 busy = IT66121_DDC_STATUS_NOACK | IT66121_DDC_STATUS_WAIT_BUS |
> -                  IT66121_DDC_STATUS_ARBI_LOSE;
> +       u32 error = IT66121_DDC_STATUS_NOACK | IT66121_DDC_STATUS_WAIT_BUS |
> +                   IT66121_DDC_STATUS_ARBI_LOSE;
> +       u32 done = IT66121_DDC_STATUS_TX_DONE;
>
> -       ret = regmap_read_poll_timeout(ctx->regmap, IT66121_DDC_STATUS_REG, val, true,
> -                                      IT66121_EDID_SLEEP_US, IT66121_EDID_TIMEOUT_US);
> +       ret = regmap_read_poll_timeout(ctx->regmap, IT66121_DDC_STATUS_REG, val,
> +                                      val & (error | done), IT66121_EDID_SLEEP_US,
> +                                      IT66121_EDID_TIMEOUT_US);
>         if (ret)
>                 return ret;
>
> -       if (val & busy)
> +       if (val & error)
>                 return -EAGAIN;
>
>         return 0;
> @@ -582,9 +584,6 @@ static int it66121_get_edid_block(void *context, u8 *buf,
>                 offset += cnt;
>                 remain -= cnt;
>
> -               /* Per programming manual, sleep here before emptying the FIFO */
> -               msleep(20);
> -
>                 ret = it66121_wait_ddc_ready(ctx);
>                 if (ret)
>                         return ret;
> --
> 2.35.1
>

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