linux-kernel - Re: [PATCH v2] drm/arm: fixes pixel clock enabled with wrong format

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Date:   Fri, 24 Apr 2020 12:00:38 +0100
From:   Emil Velikov <emil.l.velikov@...il.com>
To:     Bernard Zhao <bernard@...o.com>
Cc:     Liviu Dudau <liviu.dudau@....com>,
        Brian Starkey <brian.starkey@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        opensource.kernel@...o.com
Subject: Re: [PATCH v2] drm/arm: fixes pixel clock enabled with wrong format

Hi Bernard,

On Fri, 24 Apr 2020 at 08:15, Bernard Zhao <bernard@...o.com> wrote:
>
> The pixel clock is still enabled when the format is wrong.
> no error branch handle, and also some register is not set
> in this case, e.g: HDLCD_REG_<color>_SELECT. Maybe we
> should disable this clock and throw an warn message when
> this happened.
> With this change, the code maybe a bit more readable.
>
> Signed-off-by: Bernard Zhao <bernard@...o.com>
>
> Changes since V1:
> *add format error handle, if format is not correct, throw
> an warning message and disable this clock.
>
> Link for V1:
> *https://lore.kernel.org/patchwork/patch/1228501/
> ---
>  drivers/gpu/drm/arm/hdlcd_crtc.c | 13 +++++++++----
>  1 file changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/arm/hdlcd_crtc.c b/drivers/gpu/drm/arm/hdlcd_crtc.c
> index af67fefed38d..f3945dee2b7d 100644
> --- a/drivers/gpu/drm/arm/hdlcd_crtc.c
> +++ b/drivers/gpu/drm/arm/hdlcd_crtc.c
> @@ -96,7 +96,7 @@ static int hdlcd_set_pxl_fmt(struct drm_crtc *crtc)
>         }
>
>         if (WARN_ON(!format))
> -               return 0;
> +               return -EINVAL;
>
>         /* HDLCD uses 'bytes per pixel', zero means 1 byte */
>         btpp = (format->bits_per_pixel + 7) / 8;
> @@ -125,7 +125,7 @@ static int hdlcd_set_pxl_fmt(struct drm_crtc *crtc)
>         return 0;
>  }
>
> -static void hdlcd_crtc_mode_set_nofb(struct drm_crtc *crtc)
> +static int hdlcd_crtc_mode_set_nofb(struct drm_crtc *crtc)
>  {
>         struct hdlcd_drm_private *hdlcd = crtc_to_hdlcd_priv(crtc);
>         struct drm_display_mode *m = &crtc->state->adjusted_mode;
> @@ -162,9 +162,10 @@ static void hdlcd_crtc_mode_set_nofb(struct drm_crtc *crtc)
>
>         err = hdlcd_set_pxl_fmt(crtc);
>         if (err)
> -               return;
> +               return err;
>
>         clk_set_rate(hdlcd->clk, m->crtc_clock * 1000);
> +       return 0;
>  }
>
>  static void hdlcd_crtc_atomic_enable(struct drm_crtc *crtc,
> @@ -173,7 +174,11 @@ static void hdlcd_crtc_atomic_enable(struct drm_crtc *crtc,
>         struct hdlcd_drm_private *hdlcd = crtc_to_hdlcd_priv(crtc);
>
>         clk_prepare_enable(hdlcd->clk);
> -       hdlcd_crtc_mode_set_nofb(crtc);
> +       if (hdlcd_crtc_mode_set_nofb(crtc)) {
> +               DRM_DEBUG_KMS("Invalid format, pixel clock enable failed!\n");
> +               clk_disable_unprepare(hdlcd->clk);
> +               return;
> +       }
This doesn't seem right. As far as I can tell, the state must be
checked in the .atomic_check since .atomic_enable, intentionally,
"cannot" fail.

HTH
Emil

>         hdlcd_write(hdlcd, HDLCD_REG_COMMAND, 1);
>         drm_crtc_vblank_on(crtc);
>  }
> --
> 2.26.2
>
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> dri-devel@...ts.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

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