drm/shmem-helper: Switch to vmf_insert_pfn

We want to stop gup, which isn't the case if we use vmf_insert_page
and VM_MIXEDMAP, because that does not set pte_special.

The motivation here is to stop

drm/shmem-helper: Switch to vmf_insert_pfn

We want to stop gup, which isn't the case if we use vmf_insert_page
and VM_MIXEDMAP, because that does not set pte_special.

The motivation here is to stop get_user_pages from working on buffer
object mmaps in general. Quoting some discussion with Thomas:

On Thu, Jul 22, 2021 at 08:22:43PM +0200, Thomas Zimmermann wrote:
> Am 13.07.21 um 22:51 schrieb Daniel Vetter:
> > We want to stop gup, which isn't the case if we use vmf_insert_page
>
> What is gup?

get_user_pages. It pins memory wherever it is, which badly wreaks at least
ttm and could also cause trouble with cma allocations. In both cases
becaue we can't move/reuse these pages anymore.

Now get_user_pages fails when the memory isn't considered "normal", like
with VM_PFNMAP and using vm_insert_pfn. For consistency across all dma-buf
I'm trying (together with Christian König) to roll this out everywhere,
for fewer surprises.

E.g. for 5.14 iirc we merged a patch to do the same for ttm, where it
closes an actual bug (ttm gets really badly confused when there's suddenly
pinned pages where it thought it can move them).

cma allcoations already use VM_PFNMAP (because that's what dma_mmap is
using underneath), as is anything that's using remap_pfn_range. Worst case
we have to revert this patch for shmem helpers if it breaks something, but
I hope that's not the case. On the ttm side we've also had some fallout
that we needed to paper over with clever tricks.
v2: With this shmem gem helpers now definitely need CONFIG_MMU (0day)

v3: add more depends on MMU. For usb drivers this is a bit awkward,
but really it's correct: To be able to provide a contig mapping of
buffers to userspace on !MMU platforms we'd need to use the cma
helpers for these drivers on those platforms. As-is this wont work.

Also not exactly sure why vm_insert_page doesn't go boom, because that
definitely wont fly in practice since the pages are non-contig to
begin with.

v4: Explain the entire motivation a lot more (Thomas)

Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210812131412.2487363-2-daniel.vetter@ffwll.ch

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drm: Add GUD USB Display driver

This adds a USB display driver with the intention that it can be
used with future USB interfaced low end displays/adapters. The Linux
gadget device driver will serve

drm: Add GUD USB Display driver

This adds a USB display driver with the intention that it can be
used with future USB interfaced low end displays/adapters. The Linux
gadget device driver will serve as the canonical device implementation.

The following DRM properties are supported:
- Plane rotation
- Connector TV properties

There is also support for backlight brightness exposed as a backlight
device.

Display modes can be made available to the host driver either as DRM
display modes or through EDID. If both are present, EDID is just passed
on to userspace.

Performance is preferred over color depth, so if the device supports
RGB565, DRM_CAP_DUMB_PREFERRED_DEPTH will return 16.

If the device transfer buffer can't fit an uncompressed framebuffer
update, the update is split up into parts that do fit.

Optimal user experience is achieved by providing damage reports either by
setting FB_DAMAGE_CLIPS on pageflips or calling DRM_IOCTL_MODE_DIRTYFB.

LZ4 compression is used if the device supports it.

The driver supports a one bit monochrome transfer format: R1. This is not
implemented in the gadget driver. It is added in preparation for future
monochrome e-ink displays.

The driver is MIT licensed to smooth the path for any BSD port of the
driver.

v2:
- Use devm_drm_dev_alloc() and drmm_mode_config_init()
- drm_fbdev_generic_setup: Use preferred_bpp=0, 16 was a copy paste error
- The drm_backlight_helper is dropped, copy in the code
- Support protocol version backwards compatibility for device

v3:
- Use donated Openmoko USB pid
- Use direct compression from framebuffer when pitch matches, not only on
full frames, so split updates can benefit
- Use __le16 in struct gud_drm_req_get_connector_status
- Set edid property when the device only provides edid
- Clear compression fields in struct gud_drm_req_set_buffer
- Fix protocol version negotiation
- Remove mode->vrefresh, it's calculated

v4:
- Drop the status req polling which was a workaround for something that
turned out to be a dwc2 udc driver problem
- Add a flag for the Linux gadget to require a status request on
SET operations. Other devices will only get status req on STALL errors
- Use protocol specific error codes (Peter)
- Add a flag for devices that want to receive the entire framebuffer on
each flush (Lubomir)
- Retry a failed framebuffer flush
- If mode has changed wait for worker and clear pending damage before
queuing up new damage, fb width/height might have changed
- Increase error counter on bulk transfer failures
- Use DRM_MODE_CONNECTOR_USB
- Handle R1 kmalloc error (Peter)
- Don't try and replicate the USB get descriptor request standard for the
display descriptor (Peter)
- Make max_buffer_size optional (Peter), drop the pow2 requirement since
it's not necessary anymore.
- Don't pre-alloc a control request buffer, it was only 4k
- Let gud.h describe the whole protocol explicitly and don't let DRM
leak into it (Peter)
- Drop display mode .hskew and .vscan from the protocol
- Shorten names: s/GUD_DRM_/GUD_/ s/gud_drm_/gud_/ (Peter)
- Fix gud_pipe_check() connector picking when switching connector
- Drop gud_drm_driver_gem_create_object() cached is default now
- Retrieve USB device from struct drm_device.dev instead of keeping a
pointer
- Honour fb->offsets[0]
- Fix mode fetching when connector status is forced
- Check EDID length reported by the device
- Use drm_do_get_edid() so userspace can overrride EDID
- Set epoch counter to signal connector status change
- gud_drm_driver can be const now

v5:
- GUD_DRM_FORMAT_R1: Use non-human ascii values (Daniel)
- Change name to: GUD USB Display (Thomas, Simon)
- Change one __u32 -> __le32 in protocol header
- Always log fb flush errors, unless the previous one failed
- Run backlight update in a worker to avoid upsetting lockdep (Daniel)
- Drop backlight_ops.get_brightness, there's no readback from the device
so it doesn't really add anything.
- Set dma mask, needed by dma-buf importers

v6:
- Use obj-y in Makefile (Peter)
- Fix missing le32_to_cpu() when using GUD_DISPLAY_MAGIC (Peter)
- Set initial brightness on backlight device

v7:
- LZ4_compress_default() can return zero, check for that
- Fix memory leak in gud_pipe_check() error path (Peter)
- Improve debug and error messages (Peter)
- Don't pass length in protocol structs (Peter)
- Pass USB interface to gud_usb_control_msg() et al. (Peter)
- Improve gud_connector_fill_properties() (Peter)
- Add GUD_PIXEL_FORMAT_RGB111 (Peter)
- Remove GUD_REQ_SET_VERSION (Peter)
- Fix DRM_IOCTL_MODE_OBJ_SETPROPERTY and the rotation property
- Fix dma-buf import (Thomas)

v8:
- Forgot to filter RGB111 from reaching userspace
- Handle a device that only returns unknown device properties (Peter)
- s/GUD_PIXEL_FORMAT_RGB111/GUD_PIXEL_FORMAT_XRGB1111/ (Peter)
- Fix R1 and XRGB1111 format conversion
- Add FIXME about Big Endian being broken (Peter, Ilia)

Cc: Lubomir Rintel <lkundrak@v3.sk>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Peter Stuge <peter@stuge.se>
Tested-by: Peter Stuge <peter@stuge.se>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210313112545.37527-4-noralf@tronnes.org

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