From: Dave Stevenson dave.stevenson@raspberrypi.com
[ Upstream commit 3b45eee87da171caa28f61240ddb5c21170cda53 ]
The divider calculations tried to find the divider just faster than the clock requested. However if it required a divider of 7 then the for loop aborted without handling the "error" case, and could end up with a clock lower than requested.
The integer divider from parent PLL to DSI clock is also capable of going up to /255, not just /7 that the driver was trying. This allows for slower link frequencies on the DSI bus where the resolution permits.
Correct the loop so that we always have a clock greater than requested, and covering the whole range of dividers.
Fixes: 86c1b9eff3f2 ("drm/vc4: Adjust modes in DSI to work around the integer PLL divider.") Signed-off-by: Dave Stevenson dave.stevenson@raspberrypi.com Link: https://lore.kernel.org/r/20220613144800.326124-13-maxime@cerno.tech Signed-off-by: Maxime Ripard maxime@cerno.tech Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/vc4/vc4_dsi.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c index 0c607eb33d7e..77003ce666a4 100644 --- a/drivers/gpu/drm/vc4/vc4_dsi.c +++ b/drivers/gpu/drm/vc4/vc4_dsi.c @@ -853,11 +853,9 @@ static bool vc4_dsi_encoder_mode_fixup(struct drm_encoder *encoder, /* Find what divider gets us a faster clock than the requested * pixel clock. */ - for (divider = 1; divider < 8; divider++) { - if (parent_rate / divider < pll_clock) { - divider--; + for (divider = 1; divider < 255; divider++) { + if (parent_rate / (divider + 1) < pll_clock) break; - } }
/* Now that we've picked a PLL divider, calculate back to its