diff options
Diffstat (limited to 'drivers/gpu')
| -rw-r--r-- | drivers/gpu/drm/i915/intel_dp.c | 35 |
1 files changed, 15 insertions, 20 deletions
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c index 1f2420cbe06a..53fc1b3f6770 100644 --- a/drivers/gpu/drm/i915/intel_dp.c +++ b/drivers/gpu/drm/i915/intel_dp.c @@ -161,33 +161,23 @@ static u8 intel_dp_max_lane_count(struct intel_dp *intel_dp) return min(source_max, sink_max); } -/* - * The units on the numbers in the next two are... bizarre. Examples will - * make it clearer; this one parallels an example in the eDP spec. - * - * intel_dp_max_data_rate for one lane of 2.7GHz evaluates as: - * - * 270000 * 1 * 8 / 10 == 216000 - * - * The actual data capacity of that configuration is 2.16Gbit/s, so the - * units are decakilobits. ->clock in a drm_display_mode is in kilohertz - - * or equivalently, kilopixels per second - so for 1680x1050R it'd be - * 119000. At 18bpp that's 2142000 kilobits per second. - * - * Thus the strange-looking division by 10 in intel_dp_link_required, to - * get the result in decakilobits instead of kilobits. - */ - static int intel_dp_link_required(int pixel_clock, int bpp) { - return (pixel_clock * bpp + 9) / 10; + /* pixel_clock is in kHz, divide bpp by 8 for bit to Byte conversion */ + return DIV_ROUND_UP(pixel_clock * bpp, 8); } static int intel_dp_max_data_rate(int max_link_clock, int max_lanes) { - return (max_link_clock * max_lanes * 8) / 10; + /* max_link_clock is the link symbol clock (LS_Clk) in kHz and not the + * link rate that is generally expressed in Gbps. Since, 8 bits of data + * is transmitted every LS_Clk per lane, there is no need to account for + * the channel encoding that is done in the PHY layer here. + */ + + return max_link_clock * max_lanes; } static int @@ -3573,7 +3563,12 @@ intel_edp_init_dpcd(struct intel_dp *intel_dp) if (val == 0) break; - /* Value read is in kHz while drm clock is saved in deca-kHz */ + /* Value read multiplied by 200kHz gives the per-lane + * link rate in kHz. The source rates are, however, + * stored in terms of LS_Clk kHz. The full conversion + * back to symbols is + * (val * 200kHz)*(8/10 ch. encoding)*(1/8 bit to Byte) + */ intel_dp->sink_rates[i] = (val * 200) / 10; } intel_dp->num_sink_rates = i; |