6.17-stable review patch. If anyone has any objections, please let me know.
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From: Tomi Valkeinen tomi.valkeinen@ideasonboard.com
[ Upstream commit eea4f89b6461294ed6bea1d3285bb3f79c09a041 ]
The driver tries to calculate the value for REG_WAKEUP_TIME. However, the calculation itself is not correct, and to add on it, the resulting value is almost always larger than the field's size, so the actual result is more or less random.
According to the docs, figuring out the value for REG_WAKEUP_TIME requires HW characterization and there's no way to have a generic algorithm to come up with the value. That doesn't help at all...
However, we know that the value must be smaller than the line time, and, at least in my understanding, the proper value for it is quite small. Testing shows that setting it to 1/10 of the line time seems to work well. All video modes from my HDMI monitor work with this algorithm.
Hopefully we'll get more information on how to calculate the value, and we can then update this.
Tested-by: Parth Pancholi parth.pancholi@toradex.com Tested-by: Jayesh Choudhary j-choudhary@ti.com Reviewed-by: Devarsh Thakkar devarsht@ti.com Link: https://lore.kernel.org/r/20250723-cdns-dsi-impro-v5-11-e61cc06074c2@ideason... Signed-off-by: Tomi Valkeinen tomi.valkeinen@ideasonboard.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c index 695b6246b280f..9f1c460d5f0d4 100644 --- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c +++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c @@ -882,7 +882,13 @@ static void cdns_dsi_bridge_atomic_pre_enable(struct drm_bridge *bridge,
tx_byte_period = DIV_ROUND_DOWN_ULL((u64)NSEC_PER_SEC * 8, phy_cfg->hs_clk_rate); - reg_wakeup = (phy_cfg->hs_prepare + phy_cfg->hs_zero) / tx_byte_period; + + /* + * Estimated time [in clock cycles] to perform LP->HS on D-PHY. + * It is not clear how to calculate this, so for now, + * set it to 1/10 of the total number of clocks in a line. + */ + reg_wakeup = dsi_cfg.htotal / nlanes / 10; writel(REG_WAKEUP_TIME(reg_wakeup) | REG_LINE_DURATION(tmp), dsi->regs + VID_DPHY_TIME);