On Thu, 19 Nov 2015, Daniel Vetter <[email protected]> wrote:
> On Thu, Nov 19, 2015 at 09:58:05AM +0000, Chris Wilson wrote:
>> We have varied reports of swizzling corruption on gen4 desktop, and
>> confirmation that one at least is triggered by uneven memory banks
>> (L-shaped memory). The implication is that the swizzling varies between
>> the paired channels and the remainder of memory on the single channel. As
>> the object then has unpredictable swizzling (it will vary depending on
>> exact page allocation and may even change during the object's lifetime as
>> the pages are replaced), we have to report to userspace that the swizzling
>> is unknown.
>>
>> However, some existing userspace is buggy when it meets an unknown
>> swizzling configuration and so we need to tell another white lie and
>> mark the swizzling as NONE but report it as UNKNOWN through the extended
>> get-tiling-ioctl. See
>>
>> commit 5eb3e5a5e11d14f9deb2a4b83555443b69ab9940
>> Author: Chris Wilson <[email protected]>
>> Date: Sun Jun 28 09:19:26 2015 +0100
>>
>> drm/i915: Declare the swizzling unknown for L-shaped configurations
>>
>> for the previous example where we found that telling the truth to
>> userspace just ends up in a world of hurt.
>>
>> Also since we don't truly know what the swizzling is on the pages, we
>> need to keep them pinned to prevent swapping as the reports also
>> suggest that some gen4 devices have previously undetected bit17
>> swizzling.
>>
>> v2: Combine unknown + quirk patches to prevent userspace ever seeing
>> unknown swizzling through the normal get-tiling-ioctl. Also use the same
>> path for the existing uneven bank detection for mobile gen4.
>>
>> Reported-by: Matti Hämäläinen <[email protected]>
>> Tested--by: Matti Hämäläinen <[email protected]>
>> References: https://bugs.freedesktop.org/show_bug.cgi?id=90725
>> Signed-off-by: Chris Wilson <[email protected]>
>> Cc: Matti Hämäläinen <[email protected]>
>> Cc: Daniel Vetter <[email protected]>
>> Cc: Jani Nikula <[email protected]>
>> Cc: [email protected]
>
> Reviewed-by: Daniel Vetter <[email protected]>
Pushed to drm-intel-fixes, thanks for the patch and review.
BR,
Jani.
>
>> ---
>> drivers/gpu/drm/i915/i915_gem_fence.c | 36
>> ++++++++++++++++++++++++++---------
>> 1 file changed, 27 insertions(+), 9 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_gem_fence.c
>> b/drivers/gpu/drm/i915/i915_gem_fence.c
>> index 40a10b25956c..f010391b87f5 100644
>> --- a/drivers/gpu/drm/i915/i915_gem_fence.c
>> +++ b/drivers/gpu/drm/i915/i915_gem_fence.c
>> @@ -642,11 +642,10 @@ i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
>> }
>>
>> /* check for L-shaped memory aka modified enhanced addressing */
>> - if (IS_GEN4(dev)) {
>> - uint32_t ddc2 = I915_READ(DCC2);
>> -
>> - if (!(ddc2 & DCC2_MODIFIED_ENHANCED_DISABLE))
>> - dev_priv->quirks |= QUIRK_PIN_SWIZZLED_PAGES;
>> + if (IS_GEN4(dev) &&
>> + !(I915_READ(DCC2) & DCC2_MODIFIED_ENHANCED_DISABLE)) {
>> + swizzle_x = I915_BIT_6_SWIZZLE_UNKNOWN;
>> + swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN;
>> }
>>
>> if (dcc == 0xffffffff) {
>> @@ -675,16 +674,35 @@ i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
>> * matching, which was the case for the swizzling required in
>> * the table above, or from the 1-ch value being less than
>> * the minimum size of a rank.
>> + *
>> + * Reports indicate that the swizzling actually
>> + * varies depending upon page placement inside the
>> + * channels, i.e. we see swizzled pages where the
>> + * banks of memory are paired and unswizzled on the
>> + * uneven portion, so leave that as unknown.
>> */
>> - if (I915_READ16(C0DRB3) != I915_READ16(C1DRB3)) {
>> - swizzle_x = I915_BIT_6_SWIZZLE_NONE;
>> - swizzle_y = I915_BIT_6_SWIZZLE_NONE;
>> - } else {
>> + if (I915_READ16(C0DRB3) == I915_READ16(C1DRB3)) {
>> swizzle_x = I915_BIT_6_SWIZZLE_9_10;
>> swizzle_y = I915_BIT_6_SWIZZLE_9;
>> }
>> }
>>
>> + if (swizzle_x == I915_BIT_6_SWIZZLE_UNKNOWN ||
>> + swizzle_y == I915_BIT_6_SWIZZLE_UNKNOWN) {
>> + /* Userspace likes to explode if it sees unknown swizzling,
>> + * so lie. We will finish the lie when reporting through
>> + * the get-tiling-ioctl by reporting the physical swizzle
>> + * mode as unknown instead.
>> + *
>> + * As we don't strictly know what the swizzling is, it may be
>> + * bit17 dependent, and so we need to also prevent the pages
>> + * from being moved.
>> + */
>> + dev_priv->quirks |= QUIRK_PIN_SWIZZLED_PAGES;
>> + swizzle_x = I915_BIT_6_SWIZZLE_NONE;
>> + swizzle_y = I915_BIT_6_SWIZZLE_NONE;
>> + }
>> +
>> dev_priv->mm.bit_6_swizzle_x = swizzle_x;
>> dev_priv->mm.bit_6_swizzle_y = swizzle_y;
>> }
>> --
>> 2.6.2
>>
--
Jani Nikula, Intel Open Source Technology Center
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