[PATCH v3 2/2] media: nxp: imx8-isi: Fix scale factor calculation for hardware rounding
From: Guoniu Zhou <hidden>
Date: 2026-03-23 08:31:56
Also in:
imx, linux-media, lkml, stable
Subsystem:
media input infrastructure (v4l/dvb), nxp i.mx 8m isi driver, the rest · Maintainers:
Mauro Carvalho Chehab, Laurent Pinchart, Linus Torvalds
From: Guoniu Zhou <redacted>
The ISI hardware rounds the actual output size up to an integer, as
described in i.MX93 Reference Manual section 57.7.8 (Channel 0 Scale
Factor). The scale factor must be calculated to ensure the theoretical
output value rounds up to exactly the desired size.
Fixes: cf21f328fcaf ("media: nxp: Add i.MX8 ISI driver")
Cc: stable@vger.kernel.org
Signed-off-by: Guoniu Zhou <redacted>
---
drivers/media/platform/nxp/imx8-isi/imx8-isi-hw.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/drivers/media/platform/nxp/imx8-isi/imx8-isi-hw.c b/drivers/media/platform/nxp/imx8-isi/imx8-isi-hw.c
index 37e59d687ed7..a2edac8292a7 100644
--- a/drivers/media/platform/nxp/imx8-isi/imx8-isi-hw.c
+++ b/drivers/media/platform/nxp/imx8-isi/imx8-isi-hw.c@@ -112,7 +112,16 @@ static u32 mxc_isi_channel_scaling_ratio(unsigned int from, unsigned int to, else *dec = 8; - return min_t(u32, from * 0x1000 / (to * *dec), ISI_DOWNSCALE_THRESHOLD); + /* + * The ISI rounds output dimensions up to the next integer (i.MX93 RM + * section 57.7.8). Calculate the scale factor such that the theoretical + * output (input / scale_factor) rounds up to exactly the desired output. + * + * Example from the reference manual: Scaling 800 to 720 lines + * - scale = 0x11C8: 800/0x1C8 = 719.859375 -> 720 (correct) + * - scale = 0x11C7: 800/0x1C7 = 720.017578 -> 721 (one extra line) + */ + return min_t(u32, DIV_ROUND_UP(from * 0x1000, to * *dec), ISI_DOWNSCALE_THRESHOLD); } static void mxc_isi_channel_set_scaling(struct mxc_isi_pipe *pipe,
--
2.34.1