On Thu, Jul 30, 2020 at 10:14:43AM +0200, Thomas Zimmermann wrote:
> Hi
>
> Am 29.07.20 um 15:57 schrieb daniel@xxxxxxxx:
> > 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@xxxxxxx>
> >
> > 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.
Copying the irc discussion over: We've had that idea floating around years
ago, i915-gem even implemented in the form of pwrite/pread for usersapce.
But now all userspace moved over to mmap, so read/write has fallen out of
favour.
I'm also not sure whether we really need to fix more than just fbcon on
fbdev on drm emulation, and it feels a bit silly to add read/write just
for that. Also the is_iomem flag on the vmap (and maybe eventually on
mmap, no idea) might be able to let us fix this at least for real
eventually.
Cheers, Daniel
>
> 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
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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