linux-kernel - Re: [PATCH V4 1/3] drm/vkms: Decouple crc operations from composer

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Message-ID: <CACvgo53qkPb+3xVcUQJosnq0fSzG9kBEet2tCeLNXkkAQLSrUA@mail.gmail.com>
Date:   Tue, 2 Jun 2020 12:19:42 +0100
From:   Emil Velikov <emil.l.velikov@...il.com>
To:     Rodrigo Siqueira <Rodrigo.Siqueira@....com>
Cc:     Brian Starkey <brian.starkey@....com>,
        Liviu Dudau <liviu.dudau@....com>,
        Daniel Vetter <daniel@...ll.ch>,
        Simon Ser <contact@...rsion.fr>,
        Leandro Ribeiro <leandro.ribeiro@...labora.com>,
        Helen Koike <helen.koike@...labora.com>,
        Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>,
        "Linux-Kernel@...r. Kernel. Org" <linux-kernel@...r.kernel.org>,
        ML dri-devel <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH V4 1/3] drm/vkms: Decouple crc operations from composer

Hi Rodrigo,

On Mon, 11 May 2020 at 12:55, Rodrigo Siqueira <Rodrigo.Siqueira@....com> wrote:

> -static uint32_t _vkms_get_crc(struct vkms_composer *primary_composer,
> -                             struct vkms_composer *cursor_composer)
> +static int compose_planes(void **vaddr_out,
> +                         struct vkms_composer *primary_composer,
> +                         struct vkms_composer *cursor_composer)
>  {
>         struct drm_framebuffer *fb = &primary_composer->fb;
>         struct drm_gem_object *gem_obj = drm_gem_fb_get_obj(fb, 0);
>         struct vkms_gem_object *vkms_obj = drm_gem_to_vkms_gem(gem_obj);
> -       void *vaddr_out = kzalloc(vkms_obj->gem.size, GFP_KERNEL);
> -       u32 crc = 0;
>
> -       if (!vaddr_out) {
> -               DRM_ERROR("Failed to allocate memory for output frame.");
> -               return 0;
> +       if (!*vaddr_out) {
> +               *vaddr_out = kzalloc(vkms_obj->gem.size, GFP_KERNEL);
It would be clearer if you keep the to alloc (or not for wb) in the
caller. As-is it's very subtle and error prone.

> +               if (!*vaddr_out) {
> +                       DRM_ERROR("Cannot allocate memory for output frame.");
> +                       return -ENOMEM;
> +               }
>         }
>
> -       if (WARN_ON(!vkms_obj->vaddr)) {
> -               kfree(vaddr_out);
> -               return crc;
> -       }
> +       if (WARN_ON(!vkms_obj->vaddr))
> +               return -EINVAL;
>
> -       memcpy(vaddr_out, vkms_obj->vaddr, vkms_obj->gem.size);
> +       memcpy(*vaddr_out, vkms_obj->vaddr, vkms_obj->gem.size);
>
>         if (cursor_composer)
> -               compose_cursor(cursor_composer, primary_composer, vaddr_out);
> +               compose_cursor(cursor_composer, primary_composer, *vaddr_out);
>
> -       crc = compute_crc(vaddr_out, primary_composer);
> -
> -       kfree(vaddr_out);
> -
> -       return crc;
> +       return 0;
>  }
>
>  /**
> @@ -157,9 +153,11 @@ void vkms_composer_worker(struct work_struct *work)
>         struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
>         struct vkms_composer *primary_composer = NULL;
>         struct vkms_composer *cursor_composer = NULL;
> +       void *vaddr_out = NULL;
>         u32 crc32 = 0;
>         u64 frame_start, frame_end;
>         bool crc_pending;
> +       int ret;
>
>         spin_lock_irq(&out->composer_lock);
>         frame_start = crtc_state->frame_start;
> @@ -183,14 +181,25 @@ void vkms_composer_worker(struct work_struct *work)
>         if (crtc_state->num_active_planes == 2)
>                 cursor_composer = crtc_state->active_planes[1]->composer;
>
> -       if (primary_composer)
> -               crc32 = _vkms_get_crc(primary_composer, cursor_composer);
> +       if (!primary_composer)
> +               return;
> +
This early return changes the functionality. Namely the
drm_crtc_add_crc_entry(.... 0) is now missing. I don't recall much
about the crc to judge if that's a genuine bugfix, or newly introduced
bug.

In the former case, it should be a separate patch.

> +       ret = compose_planes(&vaddr_out, primary_composer, cursor_composer);
> +       if (ret) {
> +               if (ret == -EINVAL)
> +                       kfree(vaddr_out);
> +               return;
> +       }
> +
> +       crc32 = compute_crc(vaddr_out, primary_composer);
>
>         /*
>          * The worker can fall behind the vblank hrtimer, make sure we catch up.
>          */
>         while (frame_start <= frame_end)
>                 drm_crtc_add_crc_entry(crtc, true, frame_start++, &crc32);
> +
> +       kfree(vaddr_out);
Nit: move the free() just after compute_crc() - it's not needed for
the drm_crtc_add_crc_entry().

-Emil