linux-kernel - Re: [PATCH 4/4] drm/msm: bump UAPI version

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Date:   Fri, 30 Nov 2018 10:31:09 -0500
From:   Rob Clark <robdclark@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        David Airlie <airlied@...ux.ie>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] drm/msm: bump UAPI version

On Fri, Nov 30, 2018 at 10:12 AM Arnd Bergmann <arnd@...db.de> wrote:
>
> On Fri, Nov 30, 2018 at 4:02 PM Rob Clark <robdclark@...il.com> wrote:
> >
> > Signed-off-by: Rob Clark <robdclark@...il.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