From: Madhav Chauhan Date: Wed, 5 Apr 2017 13:04:23 +0000 (-0400) Subject: drm/i915/glk: limit pixel clock to 99% of cdclk workaround X-Git-Tag: v4.13-rc1~73^2~28^2~236 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=97f55ca5b662;p=linux.git drm/i915/glk: limit pixel clock to 99% of cdclk workaround As per BSPEC, valid cdclk values for glk are 79.2, 158.4, 316.8 Mhz. Practically we can achive only 99% of these cdclk values (HW team checking on this). So cdclk should be calculated for the given pixclk as per that otherwise it may lead to screen corruption, explained below: 1. For DSI AUO panel(1920x1200 @60) required pixclk is 157100 KHZ 2. glk_calc_cdclk returns 79200 KHZ for this pixclk, For 2PPC it will be 158400 KHZ 3. Practically 100% of the cdclk can’t be achieved, so 99% of 158400 KHZ = 156816 which is less than the desired pixlclk and causes panel corruption. v2: Rebased to new CDLCK code framework v3: Addressed review comments from Ander/Jani - Add comment in code about 99% usage of CDCLK - Calculate max dot clock as well with 99% limit v4 by Jani: - drop superfluous whitespace change - rewrite code comments to clarify v5: Added details of non-working scenario in commit message Cc: Ander Conselvan de Oliveira Cc: Ville Syrjälä Signed-off-by: Madhav Chauhan Signed-off-by: Jani Nikula Reviewed-by: Ander Conselvan de Oliveira Link: http://patchwork.freedesktop.org/patch/msgid/1491397463-13637-1-git-send-email-madhav.chauhan@intel.com --- diff --git a/drivers/gpu/drm/i915/intel_cdclk.c b/drivers/gpu/drm/i915/intel_cdclk.c index dd3ad52b7dfe..763010f8ad89 100644 --- a/drivers/gpu/drm/i915/intel_cdclk.c +++ b/drivers/gpu/drm/i915/intel_cdclk.c @@ -1071,9 +1071,15 @@ static int bxt_calc_cdclk(int max_pixclk) static int glk_calc_cdclk(int max_pixclk) { - if (max_pixclk > 2 * 158400) + /* + * FIXME: Avoid using a pixel clock that is more than 99% of the cdclk + * as a temporary workaround. Use a higher cdclk instead. (Note that + * intel_compute_max_dotclk() limits the max pixel clock to 99% of max + * cdclk.) + */ + if (max_pixclk > DIV_ROUND_UP(2 * 158400 * 99, 100)) return 316800; - else if (max_pixclk > 2 * 79200) + else if (max_pixclk > DIV_ROUND_UP(2 * 79200 * 99, 100)) return 158400; else return 79200; @@ -1664,7 +1670,11 @@ static int intel_compute_max_dotclk(struct drm_i915_private *dev_priv) int max_cdclk_freq = dev_priv->max_cdclk_freq; if (IS_GEMINILAKE(dev_priv)) - return 2 * max_cdclk_freq; + /* + * FIXME: Limiting to 99% as a temporary workaround. See + * glk_calc_cdclk() for details. + */ + return 2 * max_cdclk_freq * 99 / 100; else if (INTEL_INFO(dev_priv)->gen >= 9 || IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv)) return max_cdclk_freq;