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    Subject[PATCH v6 3/4] drm: Expand max DRM device number to full MINORBITS
    Date
    Having a limit of 64 DRM devices is not good enough for modern world
    where we have multi-GPU servers, SR-IOV virtual functions and virtual
    devices used for testing.
    Let's utilize full minor range for DRM devices.
    To avoid regressing the existing userspace, we're still maintaining the
    numbering scheme where 0-63 is used for primary, 64-127 is reserved
    (formerly for control) and 128-191 is used for render.
    For minors >= 192, we're allocating minors dynamically on a first-come,
    first-served basis.

    Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
    ---
    drivers/gpu/drm/drm_drv.c | 12 ++++++++++++
    1 file changed, 12 insertions(+)

    diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
    index 34b60196c443..c2c6e80e6b31 100644
    --- a/drivers/gpu/drm/drm_drv.c
    +++ b/drivers/gpu/drm/drm_drv.c
    @@ -121,10 +121,19 @@ static void drm_minor_alloc_release(struct drm_device *dev, void *data)
    xa_erase(drm_minor_get_xa(minor->type), minor->index);
    }

    +/*
    + * DRM used to support 64 devices, for backwards compatibility we need to maintain the
    + * minor allocation scheme where minors 0-63 are primary nodes, 64-127 are control nodes,
    + * and 128-191 are render nodes.
    + * After reaching the limit, we're allocating minors dynamically - first-come, first-serve.
    + * Accel nodes are using a distinct major, so the minors are allocated in continuous 0-MAX
    + * range.
    + */
    #define DRM_MINOR_LIMIT(t) ({ \
    typeof(t) _t = (t); \
    _t == DRM_MINOR_ACCEL ? XA_LIMIT(0, ACCEL_MAX_MINORS) : XA_LIMIT(64 * _t, 64 * _t + 63); \
    })
    +#define DRM_EXTENDED_MINOR_LIMIT XA_LIMIT(192, (1 << MINORBITS) - 1)

    static int drm_minor_alloc(struct drm_device *dev, enum drm_minor_type type)
    {
    @@ -140,6 +149,9 @@ static int drm_minor_alloc(struct drm_device *dev, enum drm_minor_type type)

    r = xa_alloc(drm_minor_get_xa(type), &minor->index,
    NULL, DRM_MINOR_LIMIT(type), GFP_KERNEL);
    + if (r == -EBUSY && (type == DRM_MINOR_PRIMARY || type == DRM_MINOR_RENDER))
    + r = xa_alloc(&drm_minors_xa, &minor->index,
    + NULL, DRM_EXTENDED_MINOR_LIMIT, GFP_KERNEL);
    if (r < 0)
    return r;

    --
    2.41.0
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