linux-kernel - [PATCH 1/2] drm/imagination: Define packed BVNCs in the uapi

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Message-ID: <20260206-bvnc-cleanup-v1-1-f3c818541fbe@imgtec.com>
Date: Fri, 6 Feb 2026 09:56:25 +0000
From: Matt Coster <matt.coster@...tec.com>
To: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard
	<mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie
	<airlied@...il.com>, Simona Vetter <simona@...ll.ch>
CC: Frank Binns <frank.binns@...tec.com>,
        Brajesh Gupta
	<brajesh.gupta@...tec.com>,
        Alessio Belle <alessio.belle@...tec.com>,
        Alexandru Dadu <alexandru.dadu@...tec.com>,
        <dri-devel@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>,
        "Matt
 Coster" <matt.coster@...tec.com>
Subject: [PATCH 1/2] drm/imagination: Define packed BVNCs in the uapi

Using the uapi-safe __GENMASK_ULL(), we can stably define the layout of
64-bit packed BVNCs. These defs replace the replicated doc comment that
appears all over the place.

Signed-off-by: Matt Coster <matt.coster@...tec.com>
---
 drivers/gpu/drm/imagination/pvr_device.h | 36 ++++++++++----------------------
 include/uapi/drm/pvr_drm.h               | 14 ++++++-------
 2 files changed, 18 insertions(+), 32 deletions(-)

diff --git a/drivers/gpu/drm/imagination/pvr_device.h b/drivers/gpu/drm/imagination/pvr_device.h
index cfda215e7428..58f0eae05ad9 100644
--- a/drivers/gpu/drm/imagination/pvr_device.h
+++ b/drivers/gpu/drm/imagination/pvr_device.h
@@ -14,7 +14,7 @@
 #include <drm/drm_file.h>
 #include <drm/drm_mm.h>
 
-#include <linux/bits.h>
+#include <linux/bitfield.h>
 #include <linux/compiler_attributes.h>
 #include <linux/compiler_types.h>
 #include <linux/device.h>
@@ -479,39 +479,25 @@ struct pvr_file {
  * @n: Number of scalable units.
  * @c: Config ID.
  *
- * The packed layout is as follows:
- *
- *    +--------+--------+--------+-------+
- *    | 63..48 | 47..32 | 31..16 | 15..0 |
- *    +========+========+========+=======+
- *    | B      | V      | N      | C     |
- *    +--------+--------+--------+-------+
+ * The packed layout follows the bitfield defined by the DRM_PVR_BVNC_* macros.
  *
  * pvr_gpu_id_to_packed_bvnc() should be used instead of this macro when a
  * &struct pvr_gpu_id is available in order to ensure proper type checking.
  *
  * Return: Packed BVNC.
  */
-/* clang-format off */
 #define PVR_PACKED_BVNC(b, v, n, c) \
-	((((u64)(b) & GENMASK_ULL(15, 0)) << 48) | \
-	 (((u64)(v) & GENMASK_ULL(15, 0)) << 32) | \
-	 (((u64)(n) & GENMASK_ULL(15, 0)) << 16) | \
-	 (((u64)(c) & GENMASK_ULL(15, 0)) <<  0))
-/* clang-format on */
+	(FIELD_PREP(DRM_PVR_BVNC_B, b) | \
+	 FIELD_PREP(DRM_PVR_BVNC_V, v) | \
+	 FIELD_PREP(DRM_PVR_BVNC_N, n) | \
+	 FIELD_PREP(DRM_PVR_BVNC_C, c))
 
 /**
  * pvr_gpu_id_to_packed_bvnc() - Packs B, V, N and C values into a 64-bit
  * unsigned integer
  * @gpu_id: GPU ID.
  *
- * The packed layout is as follows:
- *
- *    +--------+--------+--------+-------+
- *    | 63..48 | 47..32 | 31..16 | 15..0 |
- *    +========+========+========+=======+
- *    | B      | V      | N      | C     |
- *    +--------+--------+--------+-------+
+ * The packed layout follows the bitfield defined by the DRM_PVR_BVNC_* macros.
  *
  * This should be used in preference to PVR_PACKED_BVNC() when a &struct
  * pvr_gpu_id is available in order to ensure proper type checking.
@@ -527,10 +513,10 @@ pvr_gpu_id_to_packed_bvnc(const struct pvr_gpu_id *gpu_id)
 static __always_inline void
 packed_bvnc_to_pvr_gpu_id(u64 bvnc, struct pvr_gpu_id *gpu_id)
 {
-	gpu_id->b = (bvnc & GENMASK_ULL(63, 48)) >> 48;
-	gpu_id->v = (bvnc & GENMASK_ULL(47, 32)) >> 32;
-	gpu_id->n = (bvnc & GENMASK_ULL(31, 16)) >> 16;
-	gpu_id->c = bvnc & GENMASK_ULL(15, 0);
+	gpu_id->b = FIELD_GET(DRM_PVR_BVNC_B, bvnc);
+	gpu_id->v = FIELD_GET(DRM_PVR_BVNC_V, bvnc);
+	gpu_id->n = FIELD_GET(DRM_PVR_BVNC_N, bvnc);
+	gpu_id->c = FIELD_GET(DRM_PVR_BVNC_C, bvnc);
 }
 
 int pvr_device_init(struct pvr_device *pvr_dev);
diff --git a/include/uapi/drm/pvr_drm.h b/include/uapi/drm/pvr_drm.h
index ccf6c2112468..72f3f90560cf 100644
--- a/include/uapi/drm/pvr_drm.h
+++ b/include/uapi/drm/pvr_drm.h
@@ -6,6 +6,7 @@
 
 #include "drm.h"
 
+#include <linux/bits.h>
 #include <linux/const.h>
 #include <linux/types.h>
 
@@ -113,6 +114,11 @@ struct drm_pvr_obj_array {
  * DOC: PowerVR IOCTL DEV_QUERY interface
  */
 
+#define DRM_PVR_BVNC_B __GENMASK_ULL(63, 48)
+#define DRM_PVR_BVNC_V __GENMASK_ULL(47, 32)
+#define DRM_PVR_BVNC_N __GENMASK_ULL(31, 16)
+#define DRM_PVR_BVNC_C __GENMASK_ULL(15, 0)
+
 /**
  * struct drm_pvr_dev_query_gpu_info - Container used to fetch information about
  * the graphics processor.
@@ -125,13 +131,7 @@ struct drm_pvr_dev_query_gpu_info {
 	 * @gpu_id: GPU identifier.
 	 *
 	 * For all currently supported GPUs this is the BVNC encoded as a 64-bit
-	 * value as follows:
-	 *
-	 *    +--------+--------+--------+-------+
-	 *    | 63..48 | 47..32 | 31..16 | 15..0 |
-	 *    +========+========+========+=======+
-	 *    | B      | V      | N      | C     |
-	 *    +--------+--------+--------+-------+
+	 * value using the DRM_PVR_BVNC_* bitmasks.
 	 */
 	__u64 gpu_id;
 

-- 
2.52.0