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SubjectRe: [PATCH 4/4] drm/msm: bump UAPI version
On Fri, Nov 30, 2018 at 10:12 AM Arnd Bergmann <arnd@arndb.de> wrote:
>
> On Fri, Nov 30, 2018 at 4:02 PM Rob Clark <robdclark@gmail.com> wrote:
> >
> > Signed-off-by: Rob Clark <robdclark@gmail.com>
> > ---
> > drivers/gpu/drm/msm/msm_drv.c | 4 +++-
> > 1 file changed, 3 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/msm/msm_drv.c b/drivers/gpu/drm/msm/msm_drv.c
> > index 6ebbd5010722..782cc33916d6 100644
> > --- a/drivers/gpu/drm/msm/msm_drv.c
> > +++ b/drivers/gpu/drm/msm/msm_drv.c
> > @@ -36,9 +36,11 @@
> > * - 1.3.0 - adds GMEM_BASE + NR_RINGS params, SUBMITQUEUE_NEW +
> > * SUBMITQUEUE_CLOSE ioctls, and MSM_INFO_IOVA flag for
> > * MSM_GEM_INFO ioctl.
> > + * - 1.4.0 - softpin, MSM_RELOC_BO_DUMP, and GEM_INFO support to set/get
> > + * GEM object's debug name
> > */
> > #define MSM_VERSION_MAJOR 1
> > -#define MSM_VERSION_MINOR 3
> > +#define MSM_VERSION_MINOR 4
> > #define MSM_VERSION_PATCHLEVEL 0
> >
>
> I don't know the background here, but generally speaking we don't have
> version numbers for ioctls in kernel drivers. Instead, the old ioctls
> need to remain functional, but you can add new ioctl commands
> in addition.
>
> Is there something that makes this driver special?
>

The version # indicates to userspace that some new features are
supported, so that new userspace on kernel can work. For example, the
userspace side of setting a GEM obj debug name is:


static void msm_bo_set_name(struct fd_bo *bo, const char *fmt, va_list ap)
{
struct drm_msm_gem_info req = {
.handle = bo->handle,
.info = MSM_INFO_SET_NAME,
};
char buf[32];
int sz;

/* bail if kernel doesn't support this: */
if (bo->dev->version < FD_VERSION_SOFTPIN)
return;

sz = vsnprintf(buf, sizeof(buf), fmt, ap);

req.value = VOID2U64(buf);
req.len = MIN2(sz, sizeof(buf));

drmCommandWrite(bo->dev->fd, DRM_MSM_GEM_INFO, &req, sizeof(req));
}


(The old userspace on new kernel case is handled by zero padding in drm_ioctl())


BR,
-R

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