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On 10/12/17 12:53, Kevin Hao wrote: > On Thu, Oct 12, 2017 at 12:39:25PM +0300, Jyri Sarha wrote: >> We are using the vrefresh to check if we are too close to vertical >> sync to update the two framebuffer DMA registers and risk a >> collision. The vrefresh is coming from user space and normally it is >> not used for anything. For instance xserver leaves vrefresh to zero >> causing a division by zero when setting the mode. We want to make sure >> the value is valid and force its recalculation in >> tilcdc_crtc_set_mode(). >> >> Reported-by: Kevin Hao <[email protected]> >> Fixes: 11abbc9f39e0 ("drm/tilcdc: Set framebuffer DMA address to HW only if >> CRTC is enabled") >> Cc: <[email protected]> # v4.11+ >> Signed-off-by: Jyri Sarha <[email protected]> >> --- >> drivers/gpu/drm/tilcdc/tilcdc_crtc.c | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> >> diff --git a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c >> b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c >> index 704db24..aa5e87c 100644 >> --- a/drivers/gpu/drm/tilcdc/tilcdc_crtc.c >> +++ b/drivers/gpu/drm/tilcdc/tilcdc_crtc.c >> @@ -459,6 +459,16 @@ static void tilcdc_crtc_set_mode(struct drm_crtc *crtc) >> drm_framebuffer_get(fb); >> >> crtc->hwmode = crtc->state->adjusted_mode; >> + >> + /* We are using the vrefresh to check if we are too close to >> + * vertical sync to update the two framebuffer DMA registers >> + * and risk a collision. The vrefresh is coming from user >> + * space and normally it is not used for anything. We want to >> + * make sure the value is valid and force its recalculation >> + * here. >> + */ >> + crtc->hwmode.vrefresh = 0; > > Why do we need this? > The drm_mode_vrefresh() [1] checks if the vrefresh is > 0 and only calculates it if it is not. I want to make sure the value is correct by recalculating it always. This is to prevent buggy user space SW from causing undefined behaviour. Best regards, Jyri [1] int drm_mode_vrefresh(const struct drm_display_mode *mode) { int refresh = 0; unsigned int calc_val; if (mode->vrefresh > 0) refresh = mode->vrefresh; else if (mode->htotal > 0 && mode->vtotal > 0) { int vtotal; vtotal = mode->vtotal; /* work out vrefresh the value will be x1000 */ calc_val = (mode->clock * 1000); calc_val /= mode->htotal; refresh = (calc_val + vtotal / 2) / vtotal; if (mode->flags & DRM_MODE_FLAG_INTERLACE) refresh *= 2; if (mode->flags & DRM_MODE_FLAG_DBLSCAN) refresh /= 2; if (mode->vscan > 1) refresh /= mode->vscan; } return refresh; } _______________________________________________ dri-devel mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/dri-devel
