From: Guoniu Zhou <guoniu.zhou@oss•nxp.com>
To: Laurent Pinchart <laurent.pinchart@ideasonboard•com>,
Mauro Carvalho Chehab <mchehab@kernel•org>,
Shawn Guo <shawnguo@kernel•org>,
Sascha Hauer <s.hauer@pengutronix•de>,
Pengutronix Kernel Team <kernel@pengutronix•de>,
Fabio Estevam <festevam@gmail•com>,
Stefan Riedmueller <s.riedmueller@phytec•de>,
Jacopo Mondi <jacopo@jmondi•org>,
Christian Hemp <c.hemp@phytec•de>, Frank Li <frank.li@nxp•com>
Cc: Dong Aisheng <aisheng.dong@nxp•com>,
linux-media@vger•kernel.org, imx@lists•linux.dev,
linux-arm-kernel@lists•infradead.org,
linux-kernel@vger•kernel.org, Guoniu Zhou <guoniu.zhou@nxp•com>,
stable@vger•kernel.org
Subject: [PATCH v3 2/2] media: nxp: imx8-isi: Fix scale factor calculation for hardware rounding
Date: Mon, 23 Mar 2026 16:33:31 +0800 [thread overview]
Message-ID: <20260323-isi-v3-2-8df53b24e622@oss.nxp.com> (raw)
In-Reply-To: <20260323-isi-v3-0-8df53b24e622@oss.nxp.com>
From: Guoniu Zhou <guoniu.zhou@nxp•com>
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 <guoniu.zhou@nxp•com>
---
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
next prev parent reply other threads:[~2026-03-23 8:32 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-23 8:33 [PATCH v3 0/2] media: nxp: imx8-isi: Fix scaler rounding and downscaling limits Guoniu Zhou
2026-03-23 8:33 ` [PATCH v3 1/2] media: nxp: imx8-isi: Fix potential out-of-bounds issues Guoniu Zhou
2026-05-20 17:41 ` Laurent Pinchart
2026-03-23 8:33 ` Guoniu Zhou [this message]
2026-05-20 19:37 ` [PATCH v3 2/2] media: nxp: imx8-isi: Fix scale factor calculation for hardware rounding Laurent Pinchart
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