2014-12-30 Inki Dae <inki.dae@xxxxxxxxxxx>:
> On 2014년 12월 18일 22:58, Gustavo Padovan wrote:
> > From: Daniel Kurtz <djkurtz@xxxxxxxxxxxx>
> >
> > 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@xxxxxxxxxxxx>
> > Reviewed-by: Sean Paul <seanpaul@xxxxxxxxxxxx>
> > Signed-off-by: Gustavo Padovan <gustavo.padovan@xxxxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/exynos/exynos_drm_fimd.c | 26 ++++++++++++++++++++++----
> > include/video/samsung_fimd.h | 1 +
> > 2 files changed, 23 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/exynos/exynos_drm_fimd.c b/drivers/gpu/drm/exynos/exynos_drm_fimd.c
> > index e5810d1..b379182 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);
> >
> > @@ -1050,15 +1052,31 @@ static irqreturn_t fimd_irq_handler(int irq, void *dev_id)
> > if (ctx->pipe < 0 || !ctx->drm_dev)
> > goto out;
> >
> > - if (ctx->i80_if) {
> > + if (!ctx->i80_if)
> > + drm_handle_vblank(ctx->drm_dev, ctx->pipe);
> > +
> > + /*
> > + * Ensure finish_pageflip is called iff a pending flip has completed.
>
> Maybe s/iff/if
>
> > + * 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);
>
> As I already mentioned before, above codes should be called only in case
> of RGB mode until checked for i80 mode. Have you ever tested above codes
> on i80 mode?
I haven't tested it as I don't have any hardware that does i80 mode.
Let's keep this check only for !i80 then.
>
> And what if 'start_s' has a value different from one of 'start'? Is it
> ok to skip finish_pageflip request this time? Shouldn't it ensure to
> wait for that until 'start_s' has a value same as one of 'start'?
I think it is okay to skip finish_pageflip, but we could return directly
if they are different, so we keep the wait_vsync_queue running until the next
irq happens or it timeouts. How does this look to you?
Gustavo
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