@@ -529,6 +529,25 @@ void dsi_link_clk_disable_v2(struct msm_dsi_host *msm_host)
clk_disable_unprepare(msm_host->byte_clk);
}
+/**
+ * dsi_adjust_pclk_for_compression() - Adjust the pclk rate for compression case
+ * @mode: The selected mode for the DSI output
+ * @dsc: DRM DSC configuration for this DSI output
+ *
+ * Adjust the pclk rate by calculating a new hdisplay proportional to
+ * the compression ratio such that:
+ * new_hdisplay = old_hdisplay * compressed_bpp / uncompressed_bpp
+ *
+ * Porches do not need to be adjusted:
+ * - For VIDEO mode they are not compressed by DSC and are passed as is.
+ * - For CMD mode there are no actual porches. Instead these fields
+ * currently represent the overhead to the image data transfer. As such, they
+ * are calculated for the final mode parameters (after the compression) and
+ * are not to be adjusted too.
+ *
+ * FIXME: Reconsider this if/when CMD mode handling is rewritten to use
+ * refresh rate and data overhead as a starting point of the calculations.
+ */
static unsigned long dsi_adjust_pclk_for_compression(const struct drm_display_mode *mode,
const struct drm_dsc_config *dsc)
{
@@ -951,8 +970,18 @@ static void dsi_timing_setup(struct msm_dsi_host *msm_host, bool is_bonded_dsi)
if (ret)
return;
- /* Divide the display by 3 but keep back/font porch and
- * pulse width same
+ /*
+ * DPU sends 3 bytes per pclk cycle to DSI. If widebus is
+ * enabled, bus width is extended to 6 bytes.
+ *
+ * Calculate the number of pclks needed to transmit one line of
+ * the compressed data.
+
+ * The back/font porch and pulse width are kept intact. For
+ * VIDEO mode they represent timing parameters rather than
+ * actual data transfer, see the documentation for
+ * dsi_adjust_pclk_for_compression(). For CMD mode they are
+ * unused anyway.
*/
h_total -= hdisplay;
if (wide_bus_enabled && !(msm_host->mode_flags & MIPI_DSI_MODE_VIDEO))
Provide actual documentation for the pclk and hdisplay calculations in the case of DSC compression being used. Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> --- Changes since v2: - Followed suggestion by Abhinav and Marijn to improve documentatry comments. Changes since v1: - Converted dsi_adjust_pclk_for_compression() into kerneldoc (Marijn) - Added a pointer from dsi_timing_setup() docs to dsi_adjust_pclk_for_compression() (Marijn) - Fixed two typo (Marijn) --- drivers/gpu/drm/msm/dsi/dsi_host.c | 33 ++++++++++++++++++++++++++++-- 1 file changed, 31 insertions(+), 2 deletions(-)