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From:   Brian Norris <briannorris@chromium.org>
Date:   Tue, 23 Jan 2018 13:38:25 -0800
Message-ID: <CA+ASDXNDpmVdARLCD-A6nfADgmomuscpwekb8M-j=MFJhpeC4Q@mail.gmail.com>
Subject: Re: [PATCH v1 1/2] drm/bridge/synopsys: dsi: Fix dsi_host_transfer()
 return value
To:     Philippe Cornu <philippe.cornu@st.com>
Cc:     Archit Taneja <architt@codeaurora.org>,
        Andrzej Hajda <a.hajda@samsung.com>,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        David Airlie <airlied@linux.ie>,
        Benjamin Gaignard <benjamin.gaignard@linaro.org>,
        Bhumika Goyal <bhumirks@gmail.com>,
        dri-devel@lists.freedesktop.org,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Sandy Huang <hjc@rock-chips.com>,
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        linux-arm-kernel@lists.infradead.org,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@lists.infradead.org>,
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        Maxime Coquelin <mcoquelin.stm32@gmail.com>,
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        Mickael Reulier <mickael.reulier@st.com>
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Hi Philippe,

On Tue, Jan 23, 2018 at 6:26 AM, Philippe Cornu <philippe.cornu@st.com> wrote:
> The dw_mipi_dsi_host_transfer() must return the number of
> bytes transmitted/received on success instead of 0.

I'm a little confused. As of the latest drm-misc-next I'm looking at,
this still has conflicting documentation.

For ->transfer():

On success it shall return the number of bytes
 * transmitted for write packets or the number of bytes received for read
 * packets.

While mipi_dsi_generic_read() says:

 * Return: The number of bytes successfully read or a negative error code on
 * failure.

But it just returns the value that ->transfer() returns.

So I'm not sure whether the documentation is still wrong, or if the
implementation is.

Anyway, I guess maybe that isn't super-critical to *this* patch, since
we don't have RX support yet...

> Note: nb_bytes is introduced in this patch as it will be
> re-used with the future dcs/generic dsi read feature.

It feels like you could just wait to add that when you need it? It
really feels trivial and useless right now :)

Brian

>
> Signed-off-by: Philippe Cornu <philippe.cornu@st.com>
> ---
>  drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> index f458798af788..096cf5e5bb30 100644
> --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c
> @@ -403,7 +403,7 @@ static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host,
>  {
>         struct dw_mipi_dsi *dsi = host_to_dsi(host);
>         struct mipi_dsi_packet packet;
> -       int ret;
> +       int ret, nb_bytes;
>
>         ret = mipi_dsi_create_packet(&packet, msg);
>         if (ret) {
> @@ -413,7 +413,13 @@ static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host,
>
>         dw_mipi_message_config(dsi, msg);
>
> -       return dw_mipi_dsi_write(dsi, &packet);
> +       ret = dw_mipi_dsi_write(dsi, &packet);
> +       if (ret)
> +               return ret;
> +
> +       nb_bytes = packet.size;
> +
> +       return nb_bytes;
>  }
>
>  static const struct mipi_dsi_host_ops dw_mipi_dsi_host_ops = {
> --
> 2.15.1
>