Re: [PATCH 3/5] drm: Add infrastructure for vmap operations of I/O memory

[Thomas Zimmermann <tzimmermann@suse.de>]

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Hi

Am 29.07.20 um 15:57 schrieb daniel@ffwll.ch:
> On Wed, Jul 29, 2020 at 03:41:46PM +0200, Thomas Zimmermann wrote:
>> Most platforms allow for accessing framebuffer I/O memory with regular
>> load and store operations. Some platforms, such as sparc64, require
>> the use of special instructions instead.
>>
>> This patch adds vmap_iomem to struct drm_gem_object_funcs. The new
>> interface drm_client_buffer_vmap_iomem() gives DRM clients access to the
>> I/O memory buffer. The semantics of struct drm_gem_objcet_funcs.vmap
>> change slightly. It used to return system or I/O memory. Now it is
>> expected to return memory addresses that can be accessed with regular
>> load and store operations. So nothing changes for existing implementations
>> of GEM objects. If the GEM object also implements vmap_iomem, a call
>> to vmap shall only return system memory, even if I/O memory could be
>> accessed with loads and stores.
>>
>> The existing interface drm_client_buffer_vmap() shall only return memory
>> as given by drm_gem_vmap ((i.e., that is accessible via regular load and
>> store). The new interface drm_client_buffer_vmap_iomem() shall only
>> return I/O memory.
>>
>> DRM clients must map buffers by calling drm_client_buffer_vmap_iomem()
>> and drm_client_buffer_vmap() to get the buffer in I/O or system memory.
>> Each function returns NULL if the buffer is in the other memory area.
>> Depending on the type of the returned memory, clients must access the
>> framebuffer with the appropriate operations.
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
> 
> Hm I don't think this works, since for more dynamic framebuffers (like
> real big gpu ttm drivers) this is a dynamic thing, which can change every
> time we do an mmap. So I think the ttm approach of having an is_iomem flag
> is a lot better.
> 
> The trouble with that is that you don't have correct checking of sparse
> mappings, but oh well :-/ The one idea I've had to address that is using
> something like this
> 
> typedef dma_buf_addr_t {
> 	bool is_iomem;
> 	union {
> 		void __iomem *vaddr_iomem;
> 		void vaddr;
> 	};
> };
> 
> And then having a wrapper for memcpy_from_dma_buf_addr and
> memcpy_to_dma_buf_addr, which switches between memcpy and memcpy_from/toio
> depending upon the is_iomem flag.
> 
> But it's a lot more invasive unfortunately :-/

What do you think about introducing read and write callbacks for GEM
objects? Like this:

  int drm_gem_read(struct drm_gem_object *gbo, size_t off, size_t len,
void *buf);

  int drm_gem_write(struct drm_gem_object *gbo, size_t off, size_t len,
const void *buf);

The common case would by memcpy, but GEM implementations could provide
their own thing. The fbdev blit function would look like

  vaddr = drm_gem_vmap(gbo)
  if (IS_ERR(vaddr))
    return

  for (each line) {
    drm_gem_write(gbo, gbo_line_offset, line_size, src)
    gbo_line_offset = /* next line */
    src = /* next line */
  }

  drm_gem_vunmap(gbo);

The whole mess about I/O access would be self-contained.

Best regards
Thomas

> -Daniel
> 
>> ---
>>  drivers/gpu/drm/drm_client.c   | 52 ++++++++++++++++++++++++++++++++--
>>  drivers/gpu/drm/drm_gem.c      | 19 +++++++++++++
>>  drivers/gpu/drm/drm_internal.h |  1 +
>>  include/drm/drm_client.h       |  8 +++++-
>>  include/drm/drm_gem.h          | 17 +++++++++--
>>  5 files changed, 91 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_client.c b/drivers/gpu/drm/drm_client.c
>> index 495f47d23d87..b5bbe089a41e 100644
>> --- a/drivers/gpu/drm/drm_client.c
>> +++ b/drivers/gpu/drm/drm_client.c
>> @@ -327,6 +327,46 @@ void *drm_client_buffer_vmap(struct drm_client_buffer *buffer)
>>  }
>>  EXPORT_SYMBOL(drm_client_buffer_vmap);
>>  
>> +/**
>> + * drm_client_buffer_vmap_iomem - Map DRM client buffer into address space
>> + * @buffer: DRM client buffer
>> + *
>> + * This function maps a client buffer into kernel address space. If the
>> + * buffer is already mapped, it returns the mapping's address.
>> + *
>> + * Client buffer mappings are not ref'counted. Each call to
>> + * drm_client_buffer_vmap() should be followed by a call to
>> + * drm_client_buffer_vunmap(); or the client buffer should be mapped
>> + * throughout its lifetime.
>> + *
>> + * Returns:
>> + *	The mapped memory's address
>> + */
>> +void __iomem *drm_client_buffer_vmap_iomem(struct drm_client_buffer *buffer)
>> +{
>> +	void __iomem *vaddr_iomem;
>> +
>> +	if (buffer->vaddr_iomem)
>> +		return buffer->vaddr_iomem;
>> +
>> +	/*
>> +	 * FIXME: The dependency on GEM here isn't required, we could
>> +	 * convert the driver handle to a dma-buf instead and use the
>> +	 * backend-agnostic dma-buf vmap support instead. This would
>> +	 * require that the handle2fd prime ioctl is reworked to pull the
>> +	 * fd_install step out of the driver backend hooks, to make that
>> +	 * final step optional for internal users.
>> +	 */
>> +	vaddr_iomem = drm_gem_vmap_iomem(buffer->gem);
>> +	if (IS_ERR(vaddr_iomem))
>> +		return vaddr_iomem;
>> +
>> +	buffer->vaddr_iomem = vaddr_iomem;
>> +
>> +	return vaddr_iomem;
>> +}
>> +EXPORT_SYMBOL(drm_client_buffer_vmap_iomem);
>> +
>>  /**
>>   * drm_client_buffer_vunmap - Unmap DRM client buffer
>>   * @buffer: DRM client buffer
>> @@ -337,8 +377,16 @@ EXPORT_SYMBOL(drm_client_buffer_vmap);
>>   */
>>  void drm_client_buffer_vunmap(struct drm_client_buffer *buffer)
>>  {
>> -	drm_gem_vunmap(buffer->gem, buffer->vaddr);
>> -	buffer->vaddr = NULL;
>> +	drm_WARN_ON(buffer->client->dev, buffer->vaddr && buffer->vaddr_iomem);
>> +
>> +	if (buffer->vaddr) {
>> +		drm_gem_vunmap(buffer->gem, buffer->vaddr);
>> +		buffer->vaddr = NULL;
>> +	}
>> +	if (buffer->vaddr_iomem) {
>> +		drm_gem_vunmap(buffer->gem, (void *)buffer->vaddr_iomem);
>> +		buffer->vaddr_iomem = NULL;
>> +	}
>>  }
>>  EXPORT_SYMBOL(drm_client_buffer_vunmap);
>>  
>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c
>> index a57f5379fc08..a001be8c0965 100644
>> --- a/drivers/gpu/drm/drm_gem.c
>> +++ b/drivers/gpu/drm/drm_gem.c
>> @@ -1227,6 +1227,25 @@ void *drm_gem_vmap(struct drm_gem_object *obj)
>>  		vaddr = obj->funcs->vmap(obj);
>>  	else if (obj->dev->driver->gem_prime_vmap)
>>  		vaddr = obj->dev->driver->gem_prime_vmap(obj);
>> +	else if (obj->funcs && obj->funcs->vmap_iomem)
>> +		vaddr = NULL; /* requires mapping as I/O memory */
>> +	else
>> +		vaddr = ERR_PTR(-EOPNOTSUPP);
>> +
>> +	if (!vaddr)
>> +		vaddr = ERR_PTR(-ENOMEM);
>> +
>> +	return vaddr;
>> +}
>> +
>> +void __iomem *drm_gem_vmap_iomem(struct drm_gem_object *obj)
>> +{
>> +	void __iomem *vaddr;
>> +
>> +	if (obj->funcs && obj->funcs->vmap_iomem)
>> +		vaddr = obj->funcs->vmap_iomem(obj);
>> +	else if (obj->funcs && obj->funcs->vmap)
>> +		vaddr = NULL; /* requires mapping as system memory */
>>  	else
>>  		vaddr = ERR_PTR(-EOPNOTSUPP);
>>  
>> diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
>> index 8e01caaf95cc..aa1a3d4f9223 100644
>> --- a/drivers/gpu/drm/drm_internal.h
>> +++ b/drivers/gpu/drm/drm_internal.h
>> @@ -187,6 +187,7 @@ void drm_gem_print_info(struct drm_printer *p, unsigned int indent,
>>  int drm_gem_pin(struct drm_gem_object *obj);
>>  void drm_gem_unpin(struct drm_gem_object *obj);
>>  void *drm_gem_vmap(struct drm_gem_object *obj);
>> +void __iomem *drm_gem_vmap_iomem(struct drm_gem_object *obj);
>>  void drm_gem_vunmap(struct drm_gem_object *obj, void *vaddr);
>>  
>>  /* drm_debugfs.c drm_debugfs_crc.c */
>> diff --git a/include/drm/drm_client.h b/include/drm/drm_client.h
>> index 7aaea665bfc2..94aa075ee4b6 100644
>> --- a/include/drm/drm_client.h
>> +++ b/include/drm/drm_client.h
>> @@ -141,10 +141,15 @@ struct drm_client_buffer {
>>  	struct drm_gem_object *gem;
>>  
>>  	/**
>> -	 * @vaddr: Virtual address for the buffer
>> +	 * @vaddr: Virtual address for the buffer in system memory
>>  	 */
>>  	void *vaddr;
>>  
>> +	/**
>> +	 * @vaddr: Virtual address for the buffer in I/O memory
>> +	 */
>> +	void *vaddr_iomem;
>> +
>>  	/**
>>  	 * @fb: DRM framebuffer
>>  	 */
>> @@ -156,6 +161,7 @@ drm_client_framebuffer_create(struct drm_client_dev *client, u32 width, u32 heig
>>  void drm_client_framebuffer_delete(struct drm_client_buffer *buffer);
>>  int drm_client_framebuffer_flush(struct drm_client_buffer *buffer, struct drm_rect *rect);
>>  void *drm_client_buffer_vmap(struct drm_client_buffer *buffer);
>> +void __iomem *drm_client_buffer_vmap_iomem(struct drm_client_buffer *buffer);
>>  void drm_client_buffer_vunmap(struct drm_client_buffer *buffer);
>>  
>>  int drm_client_modeset_create(struct drm_client_dev *client);
>> diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h
>> index 337a48321705..bc735ff522a8 100644
>> --- a/include/drm/drm_gem.h
>> +++ b/include/drm/drm_gem.h
>> @@ -134,17 +134,28 @@ struct drm_gem_object_funcs {
>>  	 * @vmap:
>>  	 *
>>  	 * Returns a virtual address for the buffer. Used by the
>> -	 * drm_gem_dmabuf_vmap() helper.
>> +	 * drm_gem_dmabuf_vmap() helper. If the buffer is not
>> +	 * located in system memory, the function returns NULL.
>>  	 *
>>  	 * This callback is optional.
>>  	 */
>>  	void *(*vmap)(struct drm_gem_object *obj);
>>  
>> +	/**
>> +	 * @vmap_iomem:
>> +	 *
>> +	 * Returns a virtual address for the buffer. If the buffer is not
>> +	 * located in I/O memory, the function returns NULL.
>> +	 *
>> +	 * This callback is optional.
>> +	 */
>> +	void __iomem *(*vmap_iomem)(struct drm_gem_object *obj);
>> +
>>  	/**
>>  	 * @vunmap:
>>  	 *
>> -	 * Releases the address previously returned by @vmap. Used by the
>> -	 * drm_gem_dmabuf_vunmap() helper.
>> +	 * Releases the address previously returned by @vmap or @vmap_iomem.
>> +	 * Used by the drm_gem_dmabuf_vunmap() helper.
>>  	 *
>>  	 * This callback is optional.
>>  	 */
>> -- 
>> 2.27.0
>>
> 

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


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