[PATCH 6.1 251/481] drm/bridge: ti-sn65dsi83: fix CHA_DSI_CLK_RANGE rounding

Greg Kroah-Hartman
2026-03-23T16:18:13Z

6.1-stable review patch. If anyone has any objections, please let me know.

------------------

From: Luca Ceresoli <luca.ceresoli@bootlin.com>

commit 2f22702dc0fee06a240404e0f7ead5b789b253d8 upstream.

The DSI frequency must be in the range:

(CHA_DSI_CLK_RANGE * 5 MHz) <= DSI freq < ((CHA_DSI_CLK_RANGE + 1) * 5 MHz)

So the register value should point to the lower range value, but
DIV_ROUND_UP() rounds the division to the higher range value, resulting in
an excess of 1 (unless the frequency is an exact multiple of 5 MHz).

For example for a 437100000 MHz clock CHA_DSI_CLK_RANGE should be 87 (0x57):

(87 * 5 = 435) <= 437.1 < (88 * 5 = 440)

but current code returns 88 (0x58).

Fix the computation by removing the DIV_ROUND_UP().

Fixes: ceb515ba29ba ("drm/bridge: ti-sn65dsi83: Add TI SN65DSI83 and SN65DSI84 driver")
Cc: stable@vger.kernel.org
Reviewed-by: Marek Vasut <marek.vasut@mailbox.org>
Link: https://patch.msgid.link/20260226-ti-sn65dsi83-dual-lvds-fixes-and-test-pattern-v1-1-2e15f5a9a6a0@bootlin.com
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/gpu/drm/bridge/ti-sn65dsi83.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

--- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
@@ -303,9 +303,9 @@ static u8 sn65dsi83_get_dsi_range(struct
* DSI_CLK = mode clock * bpp / dsi_data_lanes / 2
* the 2 is there because the bus is DDR.
*/
- return DIV_ROUND_UP(clamp((unsigned int)mode->clock *
- mipi_dsi_pixel_format_to_bpp(ctx->dsi->format) /
- ctx->dsi->lanes / 2, 40000U, 500000U), 5000U);
+ return clamp((unsigned int)mode->clock *
+ mipi_dsi_pixel_format_to_bpp(ctx->dsi->format) /
+ ctx->dsi->lanes / 2, 40000U, 500000U) / 5000U;
}

static u8 sn65dsi83_get_dsi_div(struct sn65dsi83 *ctx)