drm/msm/dp: skip validity check for DP CTS EDID checksum

The DP CTS test for EDID last block checksum expects the checksum for
the last block, invalid or not. Skip the validity check.

For the most part (*), the EDIDs returned by drm_get_edid() will be
valid anyway, and there's the CTS workaround to get the checksum for
completely invalid EDIDs. See commit 7948fe12 ("drm/msm/dp: return
correct edid checksum after corrupted edid checksum read").

This lets us remove one user of drm_edid_block_valid() with hopes the
function can be removed altogether in the future.

(*) drm_get_edid() ignores checksum errors on CTA extensions.

Cc: Abhinav Kumar <quic_abhinavk@quicinc.com>
Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc: Kuogee Hsieh <khsieh@codeaurora.org>
Cc: Marijn Suijten <marijn.suijten@somainline.org>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Sean Paul <sean@poorly.run>
Cc: Stephen Boyd <swboyd@chromium.org>
Cc: linux-arm-msm@vger.kernel.org
Cc: freedreno@lists.freedesktop.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/555361/
Link: https://lore.kernel.org/r/20230901142034.580802-1-jani.nikula@intel.comSigned-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>

drivers/gpu/drm/msm/dp/dp_panel.c

@@ -219,26 +219,9 @@ int dp_panel_get_modes(struct dp_panel *dp_panel,
 
 static u8 dp_panel_get_edid_checksum(struct edid *edid)
 {
-	struct edid *last_block;
-	u8 *raw_edid;
-	bool is_edid_corrupt = false;
+	edid += edid->extensions;
 
-	if (!edid) {
-		DRM_ERROR("invalid edid input\n");
-		return 0;
-	}
-
-	raw_edid = (u8 *)edid;
-	raw_edid += (edid->extensions * EDID_LENGTH);
-	last_block = (struct edid *)raw_edid;
-
-	/* block type extension */
-	drm_edid_block_valid(raw_edid, 1, false, &is_edid_corrupt);
-	if (!is_edid_corrupt)
-		return last_block->checksum;
-
-	DRM_ERROR("Invalid block, no checksum\n");
-	return 0;
+	return edid->checksum;
 }
 
 void dp_panel_handle_sink_request(struct dp_panel *dp_panel)