On Wed, Feb 15, 2017 at 01:34:46AM -0800, Kenneth Graunke wrote:
> This patch makes the I915_PARAM_HAS_EXEC_CONSTANTS getparam return 0
> (indicating the optional feature is not supported), and makes execbuf
> always return -EINVAL if the flags are used.
>
> Apparently, no userspace ever shipped which used this optional feature:
> I checked the git history of Mesa, xf86-video-intel, libva, and Beignet,
> and there were zero commits showing a use of these flags. Kernel commit
> 72bfa19c8deb4 apparently introduced the feature prematurely. According
> to Chris, the intention was to use this in cairo-drm, but "the use was
> broken for gen6", so I don't think it ever happened.
>
> 'relative_constants_mode' has always been tracked per-device, but this
> has actually been wrong ever since hardware contexts were introduced, as
> the INSTPM register is saved (and automatically restored) as part of the
> render ring context. The software per-device value could therefore get
> out of sync with the hardware per-context value. This meant that using
> them is actually unsafe: a client which tried to use them could damage
> the state of other clients, causing the GPU to interpret their BO
> offsets as absolute pointers, leading to bogus memory reads.
>
> These flags were also never ported to execlist mode, making them no-ops
> on Gen9+ (which requires execlists), and Gen8 in the default mode.
>
> On Gen8+, userspace can write these registers directly, achieving the
> same effect. On Gen6-7.5, it likely makes sense to extend the command
> parser to support them. I don't think anyone wants this on Gen4-5.
>
> Based on a patch by Dave Gordon.
>
> v3: Return -ENODEV for the getparam, as this is what we do for other
> obsolete features. Suggested by Chris Wilson.
>
> Cc: [email protected]
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92448
> Signed-off-by: Kenneth Graunke <[email protected]>
> Reviewed-by: Joonas Lahtinen <[email protected]> [v2]
> Reviewed-by: Chris Wilson <[email protected]> [v2]
Reviewed-by: Chris Wilson <[email protected]>
Just give Daniel a chance to ack the ABI revert if he cares...
-Chris
> ---
> drivers/gpu/drm/i915/i915_drv.c | 4 +--
> drivers/gpu/drm/i915/i915_drv.h | 2 --
> drivers/gpu/drm/i915/i915_gem.c | 2 --
> drivers/gpu/drm/i915/i915_gem_execbuffer.c | 50
> ++----------------------------
> 4 files changed, 3 insertions(+), 55 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> index 309c29c84c54..448768cef1f6 100644
> --- a/drivers/gpu/drm/i915/i915_drv.c
> +++ b/drivers/gpu/drm/i915/i915_drv.c
> @@ -249,6 +249,7 @@ static int i915_getparam(struct drm_device *dev, void
> *data,
> case I915_PARAM_IRQ_ACTIVE:
> case I915_PARAM_ALLOW_BATCHBUFFER:
> case I915_PARAM_LAST_DISPATCH:
> + case I915_PARAM_HAS_EXEC_CONSTANTS:
> /* Reject all old ums/dri params. */
> return -ENODEV;
> case I915_PARAM_CHIPSET_ID:
> @@ -275,9 +276,6 @@ static int i915_getparam(struct drm_device *dev, void
> *data,
> case I915_PARAM_HAS_BSD2:
> value = !!dev_priv->engine[VCS2];
> break;
> - case I915_PARAM_HAS_EXEC_CONSTANTS:
> - value = INTEL_GEN(dev_priv) >= 4;
> - break;
> case I915_PARAM_HAS_LLC:
> value = HAS_LLC(dev_priv);
> break;
> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
> index 918118a268b8..8a6ba63d3f74 100644
> --- a/drivers/gpu/drm/i915/i915_drv.h
> +++ b/drivers/gpu/drm/i915/i915_drv.h
> @@ -2077,8 +2077,6 @@ struct drm_i915_private {
>
> const struct intel_device_info info;
>
> - int relative_constants_mode;
> -
> void __iomem *regs;
>
> struct intel_uncore uncore;
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 71297920fdf4..c9be0285c7cf 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -4656,8 +4656,6 @@ i915_gem_load_init(struct drm_i915_private *dev_priv)
> init_waitqueue_head(&dev_priv->gpu_error.wait_queue);
> init_waitqueue_head(&dev_priv->gpu_error.reset_queue);
>
> - dev_priv->relative_constants_mode = I915_EXEC_CONSTANTS_REL_GENERAL;
> -
> init_waitqueue_head(&dev_priv->pending_flip_queue);
>
> dev_priv->mm.interruptible = true;
> diff --git a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> index da0846fe2ad6..febb067903e9 100644
> --- a/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> +++ b/drivers/gpu/drm/i915/i915_gem_execbuffer.c
> @@ -1412,10 +1412,7 @@ execbuf_submit(struct i915_execbuffer_params *params,
> struct drm_i915_gem_execbuffer2 *args,
> struct list_head *vmas)
> {
> - struct drm_i915_private *dev_priv = params->request->i915;
> u64 exec_start, exec_len;
> - int instp_mode;
> - u32 instp_mask, *cs;
> int ret;
>
> ret = i915_gem_execbuffer_move_to_gpu(params->request, vmas);
> @@ -1426,54 +1423,11 @@ execbuf_submit(struct i915_execbuffer_params *params,
> if (ret)
> return ret;
>
> - instp_mode = args->flags & I915_EXEC_CONSTANTS_MASK;
> - instp_mask = I915_EXEC_CONSTANTS_MASK;
> - switch (instp_mode) {
> - case I915_EXEC_CONSTANTS_REL_GENERAL:
> - case I915_EXEC_CONSTANTS_ABSOLUTE:
> - case I915_EXEC_CONSTANTS_REL_SURFACE:
> - if (instp_mode != 0 && params->engine->id != RCS) {
> - DRM_DEBUG("non-0 rel constants mode on non-RCS\n");
> - return -EINVAL;
> - }
> -
> - if (instp_mode != dev_priv->relative_constants_mode) {
> - if (INTEL_INFO(dev_priv)->gen < 4) {
> - DRM_DEBUG("no rel constants on pre-gen4\n");
> - return -EINVAL;
> - }
> -
> - if (INTEL_INFO(dev_priv)->gen > 5 &&
> - instp_mode == I915_EXEC_CONSTANTS_REL_SURFACE) {
> - DRM_DEBUG("rel surface constants mode invalid
> on gen5+\n");
> - return -EINVAL;
> - }
> -
> - /* The HW changed the meaning on this bit on gen6 */
> - if (INTEL_INFO(dev_priv)->gen >= 6)
> - instp_mask &= ~I915_EXEC_CONSTANTS_REL_SURFACE;
> - }
> - break;
> - default:
> - DRM_DEBUG("execbuf with unknown constants: %d\n", instp_mode);
> + if (args->flags & I915_EXEC_CONSTANTS_MASK) {
> + DRM_DEBUG("I915_EXEC_CONSTANTS_* unsupported\n");
> return -EINVAL;
> }
>
> - if (params->engine->id == RCS &&
> - instp_mode != dev_priv->relative_constants_mode) {
> - cs = intel_ring_begin(params->request, 4);
> - if (IS_ERR(cs))
> - return PTR_ERR(cs);
> -
> - *cs++ = MI_NOOP;
> - *cs++ = MI_LOAD_REGISTER_IMM(1);
> - *cs++ = i915_mmio_reg_offset(INSTPM);
> - *cs++ = instp_mask << 16 | instp_mode;
> - intel_ring_advance(params->request, cs);
> -
> - dev_priv->relative_constants_mode = instp_mode;
> - }
> -
> if (args->flags & I915_EXEC_GEN7_SOL_RESET) {
> ret = i915_reset_gen7_sol_offsets(params->request);
> if (ret)
> --
> 2.11.1
>
--
Chris Wilson, Intel Open Source Technology Centre
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