Re: [PATCH] drm/i915: Pin the ifbdev for the info->system_base GGTT mmapping

["Boyer, Wayne" <wayne.boyer@intel.com>]

On 8/26/15, 1:23 AM, Deepak <deepak.s@linux.intel.com> wrote:


>
>
>On 08/25/2015 10:18 PM, Chris Wilson wrote:
>> A long time ago (before 3.14) we relied on a permanent pinning of the
>> ifbdev to lock the fb in place inside the GGTT. However, the
>> introduction of stealing the BIOS framebuffer and reusing its address in
>> the GGTT for the fbdev has muddied waters and we use an inherited fb.
>> However, the inherited fb is only pinned whilst it is active and we no
>> longer have an explicit pin for the info->system_base mmapping used by
>> the fbdev. The result is that after some aperture pressure the fbdev may
>> be evicted, but we continue to write the fbcon into the same GGTT
>> address - overwriting anything else that may be put into that offset.
>> The effect is most pronounced across suspend/resume as
>> intel_fbdev_set_suspend() does a full clear over the whole scanout.
>
>Yup this is a critical fix :) by keeping the internal FB pinned we avoid
>alloc of buffer within same FB GTT offset
>Reviewed-by: Deepak S <deepak.s@linux.intel.com>

Daniel,

Is there anything else that needs to happen before this gets pulled in?

Thanks,
Wayne

>
>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>> Cc: "Goel, Akash" <akash.goel@intel.com>
>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
>> Cc: Jesse Barnes <jbarnes@virtuousgeek.org>
>> Cc: stable@vger.kernel.org
>> ---
>>   drivers/gpu/drm/i915/intel_fbdev.c | 15 +++++++++++++++
>>   1 file changed, 15 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c
>>b/drivers/gpu/drm/i915/intel_fbdev.c
>> index 96476d7d7ed2..082f2938ec97 100644
>> --- a/drivers/gpu/drm/i915/intel_fbdev.c
>> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
>> @@ -215,6 +215,16 @@ static int intelfb_create(struct drm_fb_helper
>>*helper,
>>   	obj = intel_fb->obj;
>>   	size = obj->base.size;
>>   
>> +	/* The fb constructor will have already pinned us (or inherited a
>> +	 * GGTT region from the BIOS) suitable for a scanout, so
>> +	 * this should just be a no-op and increment the pin count for the
>> +	 * fbdev mmapping. It does have a useful side-effect of validating
>> +	 * the pin for fbdev's use via a GGTT mmapping.
>> +	 */
>> +	ret = i915_gem_object_ggtt_pin(obj, NULL, 0, PIN_MAPPABLE);
>> +	if (ret)
>> +		goto out_unlock;
>> +
>>   	info = drm_fb_helper_alloc_fbi(helper);
>>   	if (IS_ERR(info)) {
>>   		ret = PTR_ERR(info);
>> @@ -274,6 +284,9 @@ static int intelfb_create(struct drm_fb_helper
>>*helper,
>>   out_destroy_fbi:
>>   	drm_fb_helper_release_fbi(helper);
>>   out_unpin:
>> +	/* Once for info->screen_base mmaping... */
>> +	i915_gem_object_ggtt_unpin(obj);
>> +	/* ...and once for the intel_fb */
>>   	i915_gem_object_ggtt_unpin(obj);
>>   	drm_gem_object_unreference(&obj->base);
>>   out_unlock:
>> @@ -514,6 +527,8 @@ static const struct drm_fb_helper_funcs
>>intel_fb_helper_funcs = {
>>   static void intel_fbdev_destroy(struct drm_device *dev,
>>   				struct intel_fbdev *ifbdev)
>>   {
>> +	/* Release the pinning for the info->screen_base mmaping. */
>> +	i915_gem_object_ggtt_unpin(ifbdev->fb->obj);
>>   
>>   	drm_fb_helper_unregister_fbi(&ifbdev->helper);
>>   	drm_fb_helper_release_fbi(&ifbdev->helper);
>
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