From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ben Widawsky Subject: Re: [PATCH 3/3] drm/i915: go back to switch for VLV mem freq detection Date: Wed, 1 May 2013 18:45:18 -0700 Message-ID: <20130502014517.GB1229@bwidawsk.net> References: <1367449762-2214-1-git-send-email-jbarnes@virtuousgeek.org> <1367449762-2214-3-git-send-email-jbarnes@virtuousgeek.org> <20130502012628.GA9668@bwidawsk.net> <5181C389.9010202@whitecape.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from shiva.localdomain (unknown [209.20.75.48]) by gabe.freedesktop.org (Postfix) with ESMTP id A8F21E5C52 for ; Wed, 1 May 2013 18:42:44 -0700 (PDT) Content-Disposition: inline In-Reply-To: <5181C389.9010202@whitecape.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org Errors-To: intel-gfx-bounces+gcfxdi-intel-gfx=m.gmane.org@lists.freedesktop.org To: Kenneth Graunke Cc: intel-gfx@lists.freedesktop.org List-Id: intel-gfx@lists.freedesktop.org On Wed, May 01, 2013 at 06:38:17PM -0700, Kenneth Graunke wrote: > On 05/01/2013 06:26 PM, Ben Widawsky wrote: > >On Wed, May 01, 2013 at 04:09:22PM -0700, Jesse Barnes wrote: > >>We need to catch the invalid case and override it. > >> > >>Signed-off-by: Jesse Barnes > > Jesse, it's actually worse than that: > > Your parenthesis were off in the previous version, causing it to do > the multiplication by 266 before the bitwise-and: > > 800 + ((266 * (val >> 6)) & 3) > > This meant that you always got 800 or 802 Mhz. > > Also, even when corrected, your previous formula would return 1332 > Mhz instead of 1333 Mhz, which is slightly off and doesn't work > since you use it in explicit switch statements. > > It might be worth mentioning in the commit message. > > >>--- > >> drivers/gpu/drm/i915/intel_pm.c | 16 +++++++++++++++- > >> 1 file changed, 15 insertions(+), 1 deletion(-) > >> > >>diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c > >>index 0f4b46e..0a3b0b3 100644 > >>--- a/drivers/gpu/drm/i915/intel_pm.c > >>+++ b/drivers/gpu/drm/i915/intel_pm.c > >>@@ -2902,7 +2902,21 @@ static void valleyview_enable_rps(struct drm_device *dev) > >> GEN7_RC_CTL_TO_MODE); > >> > >> valleyview_punit_read(dev_priv, PUNIT_REG_GPU_FREQ_STS, &val); > >>- dev_priv->mem_freq = 800 + (266 * (val >> 6) & 3); > >>+ switch ((val >> 6) & 3) { > >>+ case 0: > >>+ dev_priv->mem_freq = 800; > >>+ break; > >>+ case 1: > >>+ dev_priv->mem_freq = 1066; > >>+ break; > >>+ case 2: > >>+ dev_priv->mem_freq = 1333; > >>+ break; > >>+ case 3: > >>+ DRM_ERROR("invalid mem freq, assuming 800MHz\n"); > >>+ dev_priv->mem_freq = 800; > >>+ break; > >>+ } > >> DRM_DEBUG_DRIVER("DDR speed: %d MHz", dev_priv->mem_freq); > >> > >> DRM_DEBUG_DRIVER("GPLL enabled? %s\n", val & 0x10 ? "yes" : "no"); > > > > > >I guess it doesn't handle the last case, but: > >dev_priv->mem_freq = 800 + (266 * (val))) + val/2 > > Don't use this method. Presumably Ben meant (val >> 6) here, but > even with that fix this formula returns 1067 rather than 1066, which > is wrong. You're right about the missing shift, but otherwise the formula is correct. Val is 1 in the case of 1066MHz... > > >or > > > >u32 freqs[] = {800,1066,1333,800}; > >dev_priv->mem_freq = freqs[(val >> 6) & 3]; > > I like this table based approach best. It's much more succinct than > the switch statement, and exact. Might be worth preserving the > DRM_ERROR. > > >Are two ways I would have used before making a switch block :P > > > >Just a thought, but perhaps we don't want to enable RPS if we can't > >reliably figure out the memory freq. (case 3) > > > >Reviewed-by: Ben Widawsky > > For either the switch or Ben's table: > Reviewed-by: Kenneth Graunke > > Incidentally, my Punit returns 3 here, but I believe the memory is > actually 1066. Not sure what the deal is. > > --Ken > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@lists.freedesktop.org > http://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Ben Widawsky, Intel Open Source Technology Center