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From: Tomeu Vizoso <tomeu@tomeuvizoso.net>
Date: Mon, 14 Mar 2016 14:35:22 +0100
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Subject: Re: [PATCH v15 1/3] drm: rockchip: Add basic drm driver
To: Mark Yao <mark.yao@rock-chips.com>
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On 2 December 2014 at 10:15, Mark Yao <mark.yao@rock-chips.com> wrote:
> diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> new file mode 100644
> index 0000000..e7ca25b
> --- /dev/null
> +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> @@ -0,0 +1,1455 @@
...
> +static bool vop_crtc_mode_fixup(struct drm_crtc *crtc,
> +                               const struct drm_display_mode *mode,
> +                               struct drm_display_mode *adjusted_mode)
> +{
> +       if (adjusted_mode->htotal == 0 || adjusted_mode->vtotal == 0)
> +               return false;

Hi Mark,

what's the rationale for this?

Disabling a CRTC as in [0] will cause mode_fixup() to be called with
an empty mode, failing that test.

Removing the check seems to get things working fine for a short while,
but a later modeset invariably gets the VOP to hang (as reported by
[1]).

Do you know why that check was put in place and what exactly could be
causing the hw to hang?

[0] https://cgit.freedesktop.org/xorg/app/intel-gpu-tools/tree/lib/igt_kms.c#n1616
[1] https://git.kernel.org/cgit/linux/kernel/git/next/linux-next.git/tree/drivers/gpu/drm/rockchip/rockchip_drm_vop.c#n873

Thanks,

Tomeu

> +
> +       return true;
> +}