linux-kernel - [PATCH v4 2/5] media: v4l2-common: Add helper function v4l_get_required_align_by

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Message-Id: <20250729-imx8qxp_pcam-v4-2-4dfca4ed2f87@nxp.com>
Date: Tue, 29 Jul 2025 12:06:23 -0400
From: Frank Li <Frank.Li@....com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>, 
 Mauro Carvalho Chehab <mchehab@...nel.org>, Shawn Guo <shawnguo@...nel.org>, 
 Sascha Hauer <s.hauer@...gutronix.de>, 
 Pengutronix Kernel Team <kernel@...gutronix.de>, 
 Fabio Estevam <festevam@...il.com>, Rui Miguel Silva <rmfrfs@...il.com>, 
 Martin Kepplinger <martink@...teo.de>, Purism Kernel Team <kernel@...i.sm>, 
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
 Conor Dooley <conor+dt@...nel.org>, Philipp Zabel <p.zabel@...gutronix.de>
Cc: linux-media@...r.kernel.org, imx@...ts.linux.dev, 
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 devicetree@...r.kernel.org, Frank Li <Frank.Li@....com>
Subject: [PATCH v4 2/5] media: v4l2-common: Add helper function
 v4l_get_required_align_by_bpp()

Add helper v4l_get_required_align_by_bpp() to help get width alignment
requirement. Basic replace below logic and enhance to any 2^[0..31] in
drivers/media/platform/nxp/imx-mipi-csis.c

mipi_csis_set_fmt(
{
        ...

        switch (csis_fmt->width % 8) {
        case 0:
                align = 0;
                break;
        case 4:
                align = 1;
                break;
        case 2:
        case 6:
                align = 2;
                break;
        default:
                /* 1, 3, 5, 7 */
                align = 3;
                break;
        }
	...
}

Signed-off-by: Frank Li <Frank.Li@....com>
---
changes in v4
- new patch
---
 include/media/v4l2-common.h | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/include/media/v4l2-common.h b/include/media/v4l2-common.h
index 0a43f56578bce1896cf63e29dd19f58ec0c46bed..a861d83bcd835dc854476b25919383415e5d434f 100644
--- a/include/media/v4l2-common.h
+++ b/include/media/v4l2-common.h
@@ -669,4 +669,34 @@ static inline bool v4l2_is_quant_valid(__u8 quantization)
 	       quantization == V4L2_QUANTIZATION_LIM_RANGE;
 }
 
+/**
+ * v4l_get_required_align_by_bpp - get align requirement for
+ *	v4l_bound_align_image(). (bpp * width) % (1 << align) have to be 0.
+ *	given number bpp, get width's alignment requirement. For example,
+ *	if align is 3, means require bpp * width must be multiples of 8.
+ *	    bpp     return  width's requirememnt
+ *	    0       0       none
+ *	    1       3       8 (need 3 zero bits)
+ *	    2       2       4
+ *	    3       3       8
+ *	    4       1       2
+ *	    5       3       8
+ *	    6       2       4
+ *	    7       3       8
+ * @bpp: input bpp
+ * @align: expected alignment, 2^(align).
+ *
+ * return: required alignment.
+ */
+static inline u32 v4l_get_required_align_by_bpp(u32 bpp, u32 align)
+{
+	int pos;
+
+	if (bpp == 0)
+		return 0;
+
+	pos = ffs(bpp) - 1;
+	return pos > align ? 0 : align - pos;
+}
+
 #endif /* V4L2_COMMON_H_ */

-- 
2.34.1