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Thu, 03 Oct 2019 10:20:46 -0700 (PDT) From: Douglas Anderson To: heiko@sntech.de Subject: [PATCH] drm/rockchip: Round up _before_ giving to the clock framework Date: Thu, 3 Oct 2019 10:20:24 -0700 Message-Id: <20191003102003.1.Ib233b3e706cf6317858384264d5b0ed35657456e@changeid> X-Mailer: git-send-email 2.23.0.444.g18eeb5a265-goog MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191003_102047_727915_F7812488 X-CRM114-Status: GOOD ( 18.34 ) X-Spam-Score: -0.2 (/) X-Spam-Report: SpamAssassin version 3.4.2 on bombadil.infradead.org summary: Content analysis details: (-0.2 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at https://www.dnswl.org/, no trust [2607:f8b0:4864:20:0:0:0:541 listed in] [list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.0 DKIMWL_WL_HIGH DKIMwl.org - Whitelisted High sender X-BeenThere: linux-rockchip@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Upstream kernel work for Rockchip platforms List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: David Airlie , linux-kernel@vger.kernel.org, Sandy Huang , dri-devel@lists.freedesktop.org, Douglas Anderson , linux-rockchip@lists.infradead.org, mka@chromium.org, seanpaul@chromium.org, Daniel Vetter , ryandcase@chromium.org, tfiga@chromium.org, linux-arm-kernel@lists.infradead.org Sender: "Linux-rockchip" Errors-To: linux-rockchip-bounces+patchwork-linux-rockchip=patchwork.kernel.org@lists.infradead.org I'm embarassed to say that even though I've touched vop_crtc_mode_fixup() twice and I swear I tested it, there's still a stupid glaring bug in it. Specifically, on veyron_minnie (with all the latest display timings) we want to be setting our pixel clock to 66,666,666.67 Hz and we tell userspace that's what we set, but we're actually choosing 66,000,000 Hz. This is confirmed by looking at the clock tree. The problem is that in drm_display_mode_from_videomode() we convert from Hz to kHz with: dmode->clock = vm->pixelclock / 1000; ...so when the device tree specifies a clock of 66666667 for the panel then DRM translates that to 66666000. The clock framework will always pick a clock that is _lower_ than the one requested, so it will refuse to pick 66666667 and we'll end up at 66000000. While we could try to fix drm_display_mode_from_videomode() to round to the nearest kHz and it would fix our problem, it wouldn't help if the clock we actually needed was 60,000,001 Hz. We could alternatively have DRM always round up, but maybe this would break someone else who already baked in the assumption that DRM rounds down. Let's solve this by just adding 999 Hz before calling clk_round_rate(). This should be safe and work everywhere. NOTE: if this is picked to stable, it's probably easiest to first pick commit 527e4ca3b6d1 ("drm/rockchip: Base adjustments of the mode based on prev adjustments") which shouldn't hurt in stable. Fixes: b59b8de31497 ("drm/rockchip: return a true clock rate to adjusted_mode") Signed-off-by: Douglas Anderson Reviewed-by: Sean Paul --- drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 37 +++++++++++++++++++-- 1 file changed, 34 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c index 613404f86668..84e3decb17b1 100644 --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c @@ -1040,10 +1040,41 @@ static bool vop_crtc_mode_fixup(struct drm_crtc *crtc, struct drm_display_mode *adjusted_mode) { struct vop *vop = to_vop(crtc); + unsigned long rate; - adjusted_mode->clock = - DIV_ROUND_UP(clk_round_rate(vop->dclk, - adjusted_mode->clock * 1000), 1000); + /* + * Clock craziness. + * + * Key points: + * + * - DRM works in in kHz. + * - Clock framework works in Hz. + * - Rockchip's clock driver picks the clock rate that is the + * same _OR LOWER_ than the one requested. + * + * Action plan: + * + * 1. When DRM gives us a mode, we should add 999 Hz to it. That way + * if the clock we need is 60000001 Hz (~60 MHz) and DRM tells us to + * make 60000 kHz then the clock framework will actually give us + * the right clock. + * + * NOTE: if the PLL (maybe through a divider) could actually make + * a clock rate 999 Hz higher instead of the one we want then this + * could be a problem. Unfortunately there's not much we can do + * since it's baked into DRM to use kHz. It shouldn't matter in + * practice since Rockchip PLLs are controlled by tables and + * even if there is a divider in the middle I wouldn't expect PLL + * rates in the table that are just a few kHz different. + * + * 2. Get the clock framework to round the rate for us to tell us + * what it will actually make. + * + * 3. Store the rounded up rate so that we don't need to worry about + * this in the actual clk_set_rate(). + */ + rate = clk_round_rate(vop->dclk, adjusted_mode->clock * 1000 + 999); + adjusted_mode->clock = DIV_ROUND_UP(rate, 1000); return true; }