[PATCH v3 26/32] drm/via: Add via_drm.h

Tue Jul 26 20:20:33 UTC 2022

On Wed, 27 Jul 2022 at 04:18, Thomas Zimmermann <tzimmermann at suse.de> wrote:
>
> Hi
>
> Am 26.07.22 um 19:41 schrieb Sam Ravnborg:
> > Hi Kevin.
> >
> > On Mon, Jul 25, 2022 at 04:53:53PM -0700, Kevin Brace wrote:
> >> From: Kevin Brace <kevinbrace at bracecomputerlab.com>
> >>
> >> Changed the uAPI.
> >>
> >> Signed-off-by: Kevin Brace <kevinbrace at bracecomputerlab.com>
> >
> > It would be great to have the new extensions to the UAPI documented
> > using kernel-doc.
> > As an example see: vc4_drm.h
> >
> > There are a lot of UAPI that is missing documentation, but if we do not
> > add it for new UAPI then this situation never improves.
> >
> > Please use __u32, __u64 like you see in other drm UAPI files.
> >
> > PS. If you reply to this mail, then please keep the full mail as
> > usually my mails to Kevin bounces (something with STARTTLS).
> >
> >       Sam
> >
> >> ---
> >>   include/uapi/drm/via_drm.h | 35 +++++++++++++++++++++++++++++++----
> >>   1 file changed, 31 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/include/uapi/drm/via_drm.h b/include/uapi/drm/via_drm.h
> >> index a1e125d42208..e9da45ce130a 100644
> >> --- a/include/uapi/drm/via_drm.h
> >> +++ b/include/uapi/drm/via_drm.h
> >> @@ -1,4 +1,5 @@
> >>   /*
> >> + * Copyright © 2020 Kevin Brace
> >>    * Copyright 1998-2003 VIA Technologies, Inc. All Rights Reserved.
> >>    * Copyright 2001-2003 S3 Graphics, Inc. All Rights Reserved.
> >>    *
> >> @@ -16,10 +17,10 @@
> >>    * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> >>    * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> >>    * FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT. IN NO EVENT SHALL
> >> - * VIA, S3 GRAPHICS, AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
> >> - * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> >> - * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
> >> - * DEALINGS IN THE SOFTWARE.
> >> + * THE AUTHORS, COPYRIGHT HOLDERS, AND/OR ITS SUPPLIERS BE LIABLE FOR ANY
> >> + * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT
> >> + * OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR
> >> + * THE USE OR OTHER DEALINGS IN THE SOFTWARE.
> >>    */
> > Do not mix license changes with other changes - and use SPDX tag if
> > possible for the updated license.
> > See other drm UAPI files for examples.
> >
> >
> >>   #ifndef _VIA_DRM_H_
> >>   #define _VIA_DRM_H_
> >> @@ -81,6 +82,11 @@ extern "C" {
> >>   #define DRM_VIA_DMA_BLIT        0x0e
> >>   #define DRM_VIA_BLIT_SYNC       0x0f
> >>
> >> +#define     DRM_VIA_GEM_CREATE      0x10
> >> +#define     DRM_VIA_GEM_MAP         0x11
> >> +#define     DRM_VIA_GEM_UNMAP       0x12
> >> +
> > Use the same alignment as the previous lines.
> >> +
> > Drop extra empty line.
> >
> >>   #define DRM_IOCTL_VIA_ALLOCMEM       DRM_IOWR(DRM_COMMAND_BASE + DRM_VIA_ALLOCMEM, drm_via_mem_t)
> >>   #define DRM_IOCTL_VIA_FREEMEM        DRM_IOW( DRM_COMMAND_BASE + DRM_VIA_FREEMEM, drm_via_mem_t)
> >>   #define DRM_IOCTL_VIA_AGP_INIT       DRM_IOWR(DRM_COMMAND_BASE + DRM_VIA_AGP_INIT, drm_via_agp_t)
> >> @@ -97,6 +103,10 @@ extern "C" {
> >>   #define DRM_IOCTL_VIA_DMA_BLIT    DRM_IOW(DRM_COMMAND_BASE + DRM_VIA_DMA_BLIT, drm_via_dmablit_t)
> >>   #define DRM_IOCTL_VIA_BLIT_SYNC   DRM_IOW(DRM_COMMAND_BASE + DRM_VIA_BLIT_SYNC, drm_via_blitsync_t)
> >>
> >> +#define     DRM_IOCTL_VIA_GEM_CREATE        DRM_IOWR(DRM_COMMAND_BASE + DRM_VIA_GEM_CREATE, struct drm_via_gem_create)
> >> +#define     DRM_IOCTL_VIA_GEM_MAP           DRM_IOWR(DRM_COMMAND_BASE + DRM_VIA_GEM_MAP, struct drm_via_gem_map)
> >> +#define     DRM_IOCTL_VIA_GEM_UNMAP         DRM_IOR(DRM_COMMAND_BASE + DRM_VIA_GEM_UNMAP, struct drm_via_gem_unmap)
> >> +
> > Use same alignment as previous lines.
> >
> >>   /* Indices into buf.Setup where various bits of state are mirrored per
> >>    * context and per buffer.  These can be fired at the card as a unit,
> >>    * or in a piecewise fashion as required.
> >> @@ -275,6 +285,23 @@ typedef struct drm_via_dmablit {
> >>      drm_via_blitsync_t sync;
> >>   } drm_via_dmablit_t;
> >>
> >> +struct drm_via_gem_create {
> >> +    uint64_t size;
> >> +    uint32_t alignment;
> >> +    uint32_t domain;
> >> +    uint32_t handle;
> >> +    uint64_t offset;
> >> +};
> > I do not know if this is relevant, but adding a 64 bit parameter
> > (offset) that is only 32 bit aligned looks like trouble to me.
> > I hope others that knows this better can comment here.
>
> The compiler will leave a 4-byte gap between handle and offset.
> Structure allocation guarantees a minimal alignment of 8 bytes, so the
> field alignment will be correct. It's all dependend on architecture,
> platofrm, calling convention, but that's the rule of thumb.
>
> Have a look at the tool 'pahole' to inspect data-structure alignment in
> object files. You'll find plenty of gaps in compiled structure.
>
> It's still questionable to leave the gap there. Either declare it
> explicity (e.g., __u32 empty0; )  or declare the structure with
> __attribute__((__packed__)).  Personally, I'd use the former.

It's not allowed at all to use packed or leave the gap.

https://www.kernel.org/doc/html/latest/process/botching-up-ioctls.html

The 2nd prereq covers this.

Dave.