Re: [PATCH v2 4/7] drm/simpledrm: Add support for system memory framebuffers

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Hi,

please see my review below.

Am 07.10.22 um 14:49 schrieb Thierry Reding:
From: Thierry Reding <treding@xxxxxxxxxx>

Simple framebuffers can be set up in system memory, which cannot be
requested and/or I/O remapped using the I/O resource helpers. Add a
separate code path that obtains system memory framebuffers from the
reserved memory region referenced in the memory-region property.

v2: make screen base a struct iosys_map to avoid sparse warnings

Signed-off-by: Thierry Reding <treding@xxxxxxxxxx>
---
  drivers/gpu/drm/tiny/simpledrm.c | 177 ++++++++++++++++++++++++-------
  1 file changed, 141 insertions(+), 36 deletions(-)

diff --git a/drivers/gpu/drm/tiny/simpledrm.c b/drivers/gpu/drm/tiny/simpledrm.c
index 18489779fb8a..cf36f67d22e4 100644
--- a/drivers/gpu/drm/tiny/simpledrm.c
+++ b/drivers/gpu/drm/tiny/simpledrm.c
@@ -2,6 +2,7 @@
#include <linux/clk.h>
  #include <linux/of_clk.h>
+#include <linux/of_reserved_mem.h>
  #include <linux/minmax.h>
  #include <linux/platform_data/simplefb.h>
  #include <linux/platform_device.h>
@@ -207,7 +208,9 @@ struct simpledrm_device {
  	unsigned int pitch;
/* memory management */
-	void __iomem *screen_base;
+	struct iosys_map screen_base;
+	phys_addr_t sysmem_start;
+	size_t sysmem_size;

Please store a pointer to the struct reserved_mem here. If set, we use it; if NULL, we use the memory region as before.

/* modesetting */
  	uint32_t formats[8];
@@ -441,6 +444,106 @@ static int simpledrm_device_init_regulators(struct simpledrm_device *sdev)
  }
  #endif
+/*
+ * Memory management
+ */
+
+static int simpledrm_device_init_mm_sysmem(struct simpledrm_device *sdev, phys_addr_t start,
+					   size_t size)
+{
+	struct drm_device *dev = &sdev->dev;
+	phys_addr_t end = start + size - 1;
+	void *screen_base;
+
+	drm_info(dev, "using system memory framebuffer at [%pa-%pa]\n", &start, &end);
+
+	screen_base = devm_memremap(dev->dev, start, size, MEMREMAP_WC);
+	if (!screen_base)
+		return -ENOMEM;
+
+	iosys_map_set_vaddr(&sdev->screen_base, screen_base);
+
+	return 0;
+}
+
+static int simpledrm_device_init_mm_io(struct simpledrm_device *sdev, phys_addr_t start,
+				       size_t size)
+{
+	struct drm_device *dev = &sdev->dev;
+	phys_addr_t end = start + size - 1;
+	void __iomem *screen_base;
+	struct resource *mem;
+
+	drm_info(dev, "using I/O memory framebuffer at [%pa-%pa]\n", &start, &end);
+
+	mem = devm_request_mem_region(dev->dev, start, size, sdev->dev.driver->name);
+	if (!mem) {
+		/*
+		 * We cannot make this fatal. Sometimes this comes from magic
+		 * spaces our resource handlers simply don't know about. Use
+		 * the I/O-memory resource as-is and try to map that instead.
+		 */
+		drm_warn(dev, "could not acquire memory region [%pa-%pa]\n", &start, &end);
+	} else {
+		size = resource_size(mem);
+		start = mem->start;
+	}
+
+	screen_base = devm_ioremap_wc(dev->dev, start, size);
+	if (!screen_base)
+		return -ENOMEM;
+
+	iosys_map_set_vaddr_iomem(&sdev->screen_base, screen_base);
+
+	return 0;
+}
+
+static void simpledrm_device_exit_mm(void *data)
+{
+	struct simpledrm_device *sdev = data;
+	struct drm_device *dev = &sdev->dev;
+
+	of_reserved_mem_device_release(dev->dev);
+}
+
+static int simpledrm_device_init_mm(struct simpledrm_device *sdev)
+{

No such _init_mm() helper please. Simply do everything in the _create() function.


+	int (*init)(struct simpledrm_device *sdev, phys_addr_t start, size_t size);
+	struct drm_device *dev = &sdev->dev;
+	struct platform_device *pdev = to_platform_device(dev->dev);
+	phys_addr_t start, end;
+	size_t size;
+	int ret;
+
+	ret = of_reserved_mem_device_init_by_idx(dev->dev, dev->dev->of_node, 0);

Instead of doing our own lookup of the memory node, I'd prefer to keep this function. If we encasulate it, it's better than reinventing the wheel within this driver.

A number of helpers look-up the various properties from the device tree. They are at [1] and below. We should add a new helper that reads the memory node via of_reserved_mem_device_init_by_idx(). Here's some example code

struct reserved_mem *
simplefb_get_memory_of(drm_device dev, of_node node)
{
	sdev = simpledrm_device_of_dev(dev)

	ret = of_reserved_mem_device_init_by_idx()
	if (ret)
		return ERR_PTR()

	ret = devm_add_action_or_reset(dev->dev,
		simpledrm_device_exit_mm, sdev)
	if (ret)
		return ERR_PTR()

	return sdev->rmem;
}

That wraps the rmem instance quite nicely and is similar to the rest of the code. You can call this function within the else branch at [2].

Later in _create() where we map the I/O memory, branch depending on the returned value of rmem.

if (rmem) {

  devm_aperture_acquire_from_firmware()
  devm_memremap()

} else {

  platform_get_resource()
  devm_aperture_acquire_from_firmware()
  devm_request_mem_region()
  devm_ioremap_wc()

}

Don't bother with reducing the code size. The only call that is sharable is devm_aperture_acquire_from_firmware(), which isn't worth the effort.


[1] https://elixir.bootlin.com/linux/v6.1-rc1/source/drivers/gpu/drm/tiny/simpledrm.c#L141 [2] https://elixir.bootlin.com/linux/v6.1-rc1/source/drivers/gpu/drm/tiny/simpledrm.c#L678


+	if (ret) {
+		struct resource *res;
+
+		res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+		if (!res)
+			return -EINVAL;
+
+		init = simpledrm_device_init_mm_io;
+		size = resource_size(res);
+		start = res->start;
+	} else {
+		devm_add_action_or_reset(dev->dev, simpledrm_device_exit_mm, sdev);
+		init = simpledrm_device_init_mm_sysmem;
+		start = sdev->sysmem_start;
+		size = sdev->sysmem_size;
+	}
+
+	end = start + size - 1;
+
+	ret = devm_aperture_acquire_from_firmware(dev, start, size);
+	if (ret) {
+		drm_err(dev, "could not acquire memory range [%pa-%pa]: %d\n", &start, &end, ret);
+		return ret;
+	}
+
+	return init(sdev, start, size);
+}
+
  /*
   * Modesetting
   */
@@ -491,15 +594,15 @@ static void simpledrm_primary_plane_helper_atomic_update(struct drm_plane *plane
drm_atomic_helper_damage_iter_init(&iter, old_plane_state, plane_state);
  	drm_atomic_for_each_plane_damage(&iter, &damage) {
-		struct iosys_map dst = IOSYS_MAP_INIT_VADDR(sdev->screen_base);
  		struct drm_rect dst_clip = plane_state->dst;
if (!drm_rect_intersect(&dst_clip, &damage))
  			continue;
- iosys_map_incr(&dst, drm_fb_clip_offset(sdev->pitch, sdev->format, &dst_clip));
-		drm_fb_blit(&dst, &sdev->pitch, sdev->format->format, shadow_plane_state->data, fb,
-			    &damage);
+		iosys_map_incr(&sdev->screen_base, drm_fb_clip_offset(sdev->pitch, sdev->format,
+								      &dst_clip));
+		drm_fb_blit(&sdev->screen_base, &sdev->pitch, sdev->format->format,
+			    shadow_plane_state->data, fb, &damage);
  	}
drm_dev_exit(idx);
@@ -518,7 +621,7 @@ static void simpledrm_primary_plane_helper_atomic_disable(struct drm_plane *plan
  		return;
/* Clear screen to black if disabled */
-	memset_io(sdev->screen_base, 0, sdev->pitch * sdev->mode.vdisplay);
+	iosys_map_memset(&sdev->screen_base, 0, 0, sdev->pitch * sdev->mode.vdisplay);
drm_dev_exit(idx);
  }
@@ -635,8 +738,6 @@ static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
  	struct drm_device *dev;
  	int width, height, stride;
  	const struct drm_format_info *format;
-	struct resource *res, *mem;
-	void __iomem *screen_base;
  	struct drm_plane *primary_plane;
  	struct drm_crtc *crtc;
  	struct drm_encoder *encoder;
@@ -706,35 +807,9 @@ static struct simpledrm_device *simpledrm_device_create(struct drm_driver *drv,
  	drm_dbg(dev, "framebuffer format=%p4cc, size=%dx%d, stride=%d byte\n",
  		&format->format, width, height, stride);
- /*
-	 * Memory management
-	 */
-
-	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
-	if (!res)
-		return ERR_PTR(-EINVAL);
-
-	ret = devm_aperture_acquire_from_firmware(dev, res->start, resource_size(res));
-	if (ret) {
-		drm_err(dev, "could not acquire memory range %pr: error %d\n", res, ret);
+	ret = simpledrm_device_init_mm(sdev);
+	if (ret)
  		return ERR_PTR(ret);
-	}
-
-	mem = devm_request_mem_region(&pdev->dev, res->start, resource_size(res), drv->name);
-	if (!mem) {
-		/*
-		 * We cannot make this fatal. Sometimes this comes from magic
-		 * spaces our resource handlers simply don't know about. Use
-		 * the I/O-memory resource as-is and try to map that instead.
-		 */
-		drm_warn(dev, "could not acquire memory region %pr\n", res);
-		mem = res;
-	}
-
-	screen_base = devm_ioremap_wc(&pdev->dev, mem->start, resource_size(mem));
-	if (!screen_base)
-		return ERR_PTR(-ENOMEM);
-	sdev->screen_base = screen_base;
/*
  	 * Modesetting
@@ -878,5 +953,35 @@ static struct platform_driver simpledrm_platform_driver = {
module_platform_driver(simpledrm_platform_driver); +static int simple_framebuffer_device_init(struct reserved_mem *rmem, struct device *dev)

'Simple-framebuffer' is the mechanism that provides the Linux platform device. And there's also a simplefb driver in fbdev.

The better name would be simpledrm_reserved_mem_device_init(). It makes it clear what this code belongs to.

+{
+	struct simpledrm_device *sdev = dev_get_drvdata(dev);
+
+	sdev->sysmem_start = rmem->base;
+	sdev->sysmem_size = rmem->size;

As mentioned, assign rmem directly. Should we warn here if

  platform_get_resource(pdev, IORESOURCE_MEM, 0)

returns anything but NULL?

+
+	return 0;
+}
+
+static void simple_framebuffer_device_release(struct reserved_mem *rmem, struct device *dev)

simpledrm_reserved_mem_device_release()

+{
+}

I think the caller should be updated to support callbacks of NULL here.

+
+static const struct reserved_mem_ops simple_framebuffer_ops = {

simpledrm_reserved_mem_ops

+	.device_init = simple_framebuffer_device_init,
+	.device_release = simple_framebuffer_device_release,
+};
+
+static int simple_framebuffer_init(struct reserved_mem *rmem)

simpledrm_reserved_mem_init()

+{
+	pr_info("framebuffer memory at %pa, size %lu bytes\n", &rmem->base,

pr_debug() please.

+		(unsigned long)rmem->size);
+
+	rmem->ops = &simple_framebuffer_ops;
+
+	return 0;
+}
+RESERVEDMEM_OF_DECLARE(simple_framebuffer, "framebuffer", simple_framebuffer_init);

 (simpledrm_reserved_mem, framebuffer, simpledrm_reserved_mem_init)

, I guess.

Best regards
Thomas

+
  MODULE_DESCRIPTION(DRIVER_DESC);
  MODULE_LICENSE("GPL v2");

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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