From 41ed08a9f69534914977520b601f6b1551841ad8 Mon Sep 17 00:00:00 2001 From: Dmitry Osipenko Date: Tue, 2 Mar 2021 16:15:06 +0300 Subject: [PATCH] drm/tegra: dc: Don't set PLL clock to 0Hz [ Upstream commit f8fb97c915954fc6de6513cdf277103b5c6df7b3 ] RGB output doesn't allow to change parent clock rate of the display and PCLK rate is set to 0Hz in this case. The tegra_dc_commit_state() shall not set the display clock to 0Hz since this change propagates to the parent clock. The DISP clock is defined as a NODIV clock by the tegra-clk driver and all NODIV clocks use the CLK_SET_RATE_PARENT flag. This bug stayed unnoticed because by default PLLP is used as the parent clock for the display controller and PLLP silently skips the erroneous 0Hz rate changes because it always has active child clocks that don't permit rate changes. The PLLP isn't acceptable for some devices that we want to upstream (like Samsung Galaxy Tab and ASUS TF700T) due to a display panel clock rate requirements that can't be fulfilled by using PLLP and then the bug pops up in this case since parent clock is set to 0Hz, killing the display output. Don't touch DC clock if pclk=0 in order to fix the problem. Signed-off-by: Dmitry Osipenko Signed-off-by: Thierry Reding Signed-off-by: Sasha Levin --- drivers/gpu/drm/tegra/dc.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/tegra/dc.c b/drivers/gpu/drm/tegra/dc.c index 965088afcfade..03adb4cf325b9 100644 --- a/drivers/gpu/drm/tegra/dc.c +++ b/drivers/gpu/drm/tegra/dc.c @@ -1670,6 +1670,11 @@ static void tegra_dc_commit_state(struct tegra_dc *dc, dev_err(dc->dev, "failed to set clock rate to %lu Hz\n", state->pclk); + + err = clk_set_rate(dc->clk, state->pclk); + if (err < 0) + dev_err(dc->dev, "failed to set clock %pC to %lu Hz: %d\n", + dc->clk, state->pclk, err); } DRM_DEBUG_KMS("rate: %lu, div: %u\n", clk_get_rate(dc->clk), @@ -1680,11 +1685,6 @@ static void tegra_dc_commit_state(struct tegra_dc *dc, value = SHIFT_CLK_DIVIDER(state->div) | PIXEL_CLK_DIVIDER_PCD1; tegra_dc_writel(dc, value, DC_DISP_DISP_CLOCK_CONTROL); } - - err = clk_set_rate(dc->clk, state->pclk); - if (err < 0) - dev_err(dc->dev, "failed to set clock %pC to %lu Hz: %d\n", - dc->clk, state->pclk, err); } static void tegra_dc_stop(struct tegra_dc *dc) -- 2.47.3