linux-kernel - [PATCH RFC v3 09/14] drm/vkms: Introduce configfs for plane format

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Message-Id: <20250121-google-config-fs-v3-9-8154a6945142@bootlin.com>
Date: Tue, 21 Jan 2025 15:34:53 +0100
From: Louis Chauvet <louis.chauvet@...tlin.com>
To: Rodrigo Siqueira <rodrigosiqueiramelo@...il.com>, 
 Melissa Wen <melissa.srw@...il.com>, 
 Maíra Canal <mairacanal@...eup.net>, 
 Haneen Mohammed <hamohammed.sa@...il.com>, 
 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>, 
 Simona Vetter <simona.vetter@...ll.ch>
Cc: jose.exposito89@...il.com, dri-devel@...ts.freedesktop.org, 
 arthurgrillo@...eup.net, linux-kernel@...r.kernel.org, 
 jeremie.dautheribes@...tlin.com, miquel.raynal@...tlin.com, 
 thomas.petazzoni@...tlin.com, seanpaul@...gle.com, nicolejadeyee@...gle.com, 
 Louis Chauvet <louis.chauvet@...tlin.com>
Subject: [PATCH RFC v3 09/14] drm/vkms: Introduce configfs for plane format

To allows the userspace to test many hardware configuration, introduce a
new interface to configure the available formats per planes. VKMS
supports many formats, so the userspace can choose any combination of
them.

The supported formats are configured by writing in the file
supported_formats:
- `+*` - Add all available formats
- `-*` - Remove all formats
- `+<fourcc>` - Add the format (for example `+AR24` to add ARGB8888
  format)
- `-<FOURCC>` - Remove the format

The current interface is:
/config/vkms
        DEVICE_1
        ┣━ enable
        ┗━ planes
           ┗━ PLANE_1
              ┗━ supported_formats

Signed-off-by: Louis Chauvet <louis.chauvet@...tlin.com>
---
 drivers/gpu/drm/vkms/vkms_configfs.c | 75 ++++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)

diff --git a/drivers/gpu/drm/vkms/vkms_configfs.c b/drivers/gpu/drm/vkms/vkms_configfs.c
index 5f416260f209fc98939f8addd175e5c3b8e35353..eeb0c1e1b225f2a1a35ac6deb9457b90ba6542e5 100644
--- a/drivers/gpu/drm/vkms/vkms_configfs.c
+++ b/drivers/gpu/drm/vkms/vkms_configfs.c
@@ -153,14 +153,89 @@ static ssize_t plane_default_rotation_store(struct config_item *item,
 	return count;
 }
 
+static ssize_t plane_supported_formats_show(struct config_item *item, char *page)
+{
+	struct vkms_config_plane *plane = plane_item_to_vkms_configfs_plane(item)->vkms_config_plane;
+	struct vkms_configfs_device *vkms_configfs = plane_item_to_vkms_configfs_device(item);
+
+	page[0] = '\0';
+
+	scoped_guard(mutex, &vkms_configfs->lock)
+	{
+		for (int i = 0; i < plane->supported_formats_count; i++) {
+			char tmp[6] = { 0 };
+			const ssize_t ret = snprintf(tmp, ARRAY_SIZE(tmp), "%.*s\n",
+					       (int)sizeof(plane->supported_formats[i]),
+					       (char *)&plane->supported_formats[i]);
+			if (ret < 0)
+				return ret;
+			/* Limitation of ConfigFS attributes, an attribute can't be bigger than PAGE_SIZE */
+			if (ret + strlen(page) > PAGE_SIZE - 1)
+				return -ENOMEM;
+			strncat(page, tmp, ARRAY_SIZE(tmp));
+		}
+	}
+
+	return strlen(page);
+}
+
+static ssize_t plane_supported_formats_store(struct config_item *item,
+					     const char *page, size_t count)
+{
+	struct vkms_config_plane *plane = plane_item_to_vkms_configfs_plane(item)->vkms_config_plane;
+	struct vkms_configfs_device *vkms_configfs = plane_item_to_vkms_configfs_device(item);
+	int ret = 0;
+	int ptr = 0;
+
+	scoped_guard(mutex, &vkms_configfs->lock)
+	{
+		while (ptr < count) {
+			if (page[ptr] == '+') {
+				char tmp[4] = { ' ', ' ', ' ', ' ' };
+
+				memcpy(tmp, &page[ptr + 1], min(sizeof(tmp), count - (ptr + 1)));
+				if (tmp[0] == '*') {
+					ret = vkms_config_plane_add_all_formats(plane);
+					if (ret)
+						return ret;
+					ptr += 1;
+				} else {
+					ret = vkms_config_plane_add_format(plane, *(int *)tmp);
+					if (ret)
+						return ret;
+					ptr += 4;
+				}
+			} else if (page[ptr] == '-') {
+				char tmp[4] = { ' ', ' ', ' ', ' ' };
+
+				memcpy(tmp, &page[ptr + 1], min(sizeof(tmp), count - (ptr + 1)));
+				if (tmp[0] == '*') {
+					vkms_config_plane_remove_all_formats(plane);
+					ptr += 1;
+				} else {
+					vkms_config_plane_remove_format(plane, *(int *)tmp);
+
+					ptr += 4;
+				}
+			}
+			/* Skip anything that is not a + or a - */
+			ptr += 1;
+		}
+	}
+
+	return count;
+}
+
 CONFIGFS_ATTR(plane_, type);
 CONFIGFS_ATTR(plane_, supported_rotations);
 CONFIGFS_ATTR(plane_, default_rotation);
+CONFIGFS_ATTR(plane_, supported_formats);
 
 static struct configfs_attribute *plane_attrs[] = {
 	&plane_attr_type,
 	&plane_attr_supported_rotations,
 	&plane_attr_default_rotation,
+	&plane_attr_supported_formats,
 	NULL,
 };
 

-- 
2.47.1