[PATCH v2] drm/exynos/fimd: only finish pageflip if START == START_S

[Inki Dae]

On 2014년 12월 11일 01:57, Gustavo Padovan wrote:
> From: Daniel Kurtz <djkurtz at chromium.org>
> 
> A framebuffer gets committed to FIMD's default window like this:
>  exynos_drm_crtc_update()
>   exynos_plane_commit()
>    fimd_win_commit()
> 
> fimd_win_commit() programs BUF_START[0].  At each vblank, FIMD hardware
> copies the value from BUF_START to BUF_START_S (BUF_START's shadow
> register), starts scanning out from BUF_START_S, and asserts its irq.
> 
> This irq is handled by fimd_irq_handler(), which calls
> exynos_drm_crtc_finish_pageflip() to free the old buffer that FIMD just
> finished scanning out, and potentially commit the next pending flip.
> 
> There is a race, however, if fimd_win_commit() programs BUF_START(0)
> between the actual vblank irq, and its corresponding fimd_irq_handler().
> 
>  => FIMD vblank: BUF_START_S[0] := BUF_START[0], and irq asserted
>  | => fimd_win_commit(0) writes new BUF_START[0]
>  |    exynos_drm_crtc_try_do_flip() marks exynos_fb as prepared
>  => fimd_irq_handler()
>     exynos_drm_crtc_finish_pageflip() sees prepared exynos_fb,
>          and unmaps "old" fb
>  ==> but, since BUF_START_S[0] still points to that "old" fb...
>  ==> FIMD iommu fault
> 
> This patch ensures that fimd_irq_handler() only calls
> exynos_drm_crtc_finish_pageflip() if any previously scheduled flip
> has really completed.
> 
> This works because exynos_drm_crtc's flip fifo ensures that
> fimd_win_commit() is never called more than once per
> exynos_drm_crtc_finish_pageflip().
> 
> Signed-off-by: Daniel Kurtz <djkurtz at chromium.org>
> Reviewed-by: Sean Paul <seanpaul at chromium.org>
> Signed-off-by: Gustavo Padovan <gustavo.padovan at collabora.co.uk>
> ---
>  drivers/gpu/drm/exynos/exynos_drm_fimd.c | 31 ++++++++++++++++++++++++-------
>  include/video/samsung_fimd.h             |  1 +
>  2 files changed, 25 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/gpu/drm/exynos/exynos_drm_fimd.c b/drivers/gpu/drm/exynos/exynos_drm_fimd.c
> index e5810d1..95bac27 100644
> --- a/drivers/gpu/drm/exynos/exynos_drm_fimd.c
> +++ b/drivers/gpu/drm/exynos/exynos_drm_fimd.c
> @@ -55,6 +55,7 @@
>  #define VIDOSD_D(win)		(VIDOSD_BASE + 0x0C + (win) * 16)
>  
>  #define VIDWx_BUF_START(win, buf)	(VIDW_BUF_START(buf) + (win) * 8)
> +#define VIDWx_BUF_START_S(win, buf)     (VIDW_BUF_START_S(buf) + (win) * 8)
>  #define VIDWx_BUF_END(win, buf)		(VIDW_BUF_END(buf) + (win) * 8)
>  #define VIDWx_BUF_SIZE(win, buf)	(VIDW_BUF_SIZE(buf) + (win) * 4)
>  
> @@ -1039,6 +1040,7 @@ static irqreturn_t fimd_irq_handler(int irq, void *dev_id)
>  {
>  	struct fimd_context *ctx = (struct fimd_context *)dev_id;
>  	u32 val, clear_bit;
> +	u32 start, start_s;
>  
>  	val = readl(ctx->regs + VIDINTCON1);
>  
> @@ -1051,19 +1053,34 @@ static irqreturn_t fimd_irq_handler(int irq, void *dev_id)
>  		goto out;
>  
>  	if (ctx->i80_if) {
> -		exynos_drm_crtc_finish_pageflip(ctx->drm_dev, ctx->pipe);
> -
>  		/* Exits triggering mode */
>  		atomic_set(&ctx->triggering, 0);
>  	} else {
>  		drm_handle_vblank(ctx->drm_dev, ctx->pipe);
> +	}
> +
> +	/*
> +	 * Ensure finish_pageflip is called iff a pending flip has completed.
> +	 * This works around a race between a page_flip request and the latency
> +	 * between vblank interrupt and this irq_handler:
> +	 *   => FIMD vblank: BUF_START_S[0] := BUF_START[0], and asserts irq
> +	 *   | => fimd_win_commit(0) writes new BUF_START[0]
> +	 *   |    exynos_drm_crtc_try_do_flip() marks exynos_fb as prepared
> +	 *   => fimd_irq_handler()
> +	 *       exynos_drm_crtc_finish_pageflip() sees prepared exynos_fb,
> +	 *           and unmaps "old" fb
> +	 *   ==> but, since BUF_START_S[0] still points to that "old" fb...
> +	 *   ==> FIMD iommu fault
> +	 */
> +	start = readl(ctx->regs + VIDWx_BUF_START(0, 0));
> +	start_s = readl(ctx->regs + VIDWx_BUF_START_S(0, 0));
> +	if (start == start_s)
>  		exynos_drm_crtc_finish_pageflip(ctx->drm_dev, ctx->pipe);

Did you test abvoe codes on I80 mode? If not so, I think this function
should be called only in case of RGB mode until checked.

>  
> -		/* set wait vsync event to zero and wake up queue. */
> -		if (atomic_read(&ctx->wait_vsync_event)) {
> -			atomic_set(&ctx->wait_vsync_event, 0);
> -			wake_up(&ctx->wait_vsync_queue);
> -		}
> +	/* set wait vsync event to zero and wake up queue. */
> +	if (atomic_read(&ctx->wait_vsync_event)) {
> +		atomic_set(&ctx->wait_vsync_event, 0);
> +		wake_up(&ctx->wait_vsync_queue);

And in case of i80 mode, wait_vsync_queue will be waked up by
fimd_te_handler so I think above relevant codes should be called only in
case of RGB mode.

Thanks,
Inki Dae

>  	}
>  
>  out:
> diff --git a/include/video/samsung_fimd.h b/include/video/samsung_fimd.h
> index a20e4a3..f81d081 100644
> --- a/include/video/samsung_fimd.h
> +++ b/include/video/samsung_fimd.h
> @@ -291,6 +291,7 @@
>  
>  /* Video buffer addresses */
>  #define VIDW_BUF_START(_buff)			(0xA0 + ((_buff) * 8))
> +#define VIDW_BUF_START_S(_buff)                 (0x40A0 + ((_buff) * 8))
>  #define VIDW_BUF_START1(_buff)			(0xA4 + ((_buff) * 8))
>  #define VIDW_BUF_END(_buff)			(0xD0 + ((_buff) * 8))
>  #define VIDW_BUF_END1(_buff)			(0xD4 + ((_buff) * 8))
>