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drm/i915/gvt: Prevent divided by zero when calculating refresh rate

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To get refresh rate as vblank timer period and keep the precision, the
calculation of rate is multiplied by 1000. However old logic was using:
rate = pixel clock / (h * v / 1000). When the h/v total is invalid, like
all 0, h * v / 1000 will be rounded to 0, which leads to a divided by 0
fault.

0 H/V are already checked above. Instead of divide after divide, refine
the calculation to divide after multiply: "pixel clock * 1000 / (h * v)"
Guest driver should guarantee the correctness of the timing regs' value.

Fixes: 6a4500c7b8 ("drm/i915/gvt: Get accurate vGPU virtual display refresh rate from vreg")
Reported-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Colin Xu <colin.xu@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20210416083355.159305-1-colin.xu@intel.com
Reviewed-by: Zhenyu Wang <zhenyuw@linux.intel.com>
This commit is contained in:
Colin Xu 2021-04-16 16:33:55 +08:00 committed by Zhenyu Wang
parent e65a4d3784
commit d385c16173
1 changed files with 3 additions and 3 deletions
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6
drivers/gpu/drm/i915/gvt/handlers.c
View file

@ -669,8 +669,8 @@ static void vgpu_update_refresh_rate(struct intel_vgpu *vgpu)
link_n = vgpu_vreg_t(vgpu, PIPE_LINK_N1(TRANSCODER_A));
/* Get H/V total from transcoder timing */
htotal = (vgpu_vreg_t(vgpu, HTOTAL(TRANSCODER_A)) >> TRANS_HTOTAL_SHIFT) + 1;
vtotal = (vgpu_vreg_t(vgpu, VTOTAL(TRANSCODER_A)) >> TRANS_VTOTAL_SHIFT) + 1;
htotal = (vgpu_vreg_t(vgpu, HTOTAL(TRANSCODER_A)) >> TRANS_HTOTAL_SHIFT);
vtotal = (vgpu_vreg_t(vgpu, VTOTAL(TRANSCODER_A)) >> TRANS_VTOTAL_SHIFT);
if (dp_br && link_n && htotal && vtotal) {
u64 pixel_clk = 0;
@ -682,7 +682,7 @@ static void vgpu_update_refresh_rate(struct intel_vgpu *vgpu)
pixel_clk *= MSEC_PER_SEC;
/* Calcuate refresh rate by (pixel_clk / (h_total * v_total)) */
new_rate = DIV64_U64_ROUND_CLOSEST(pixel_clk, div64_u64(mul_u32_u32(htotal, vtotal), MSEC_PER_SEC));
new_rate = DIV64_U64_ROUND_CLOSEST(mul_u64_u32_shr(pixel_clk, MSEC_PER_SEC, 0), mul_u32_u32(htotal + 1, vtotal + 1));
if (*old_rate != new_rate)
*old_rate = new_rate;