[PATCH 3/3] arm64: dts: meson: Describe G12b GPU as coherent

[Steven Price]

On 05/10/2020 09:15, Boris Brezillon wrote:
> Hi Robin, Neil,
> 
> On Wed, 16 Sep 2020 10:26:43 +0200
> Neil Armstrong <narmstrong at baylibre.com> wrote:
> 
>> Hi Robin,
>>
>> On 16/09/2020 01:51, Robin Murphy wrote:
>>> According to a downstream commit I found in the Khadas vendor kernel,
>>> the GPU on G12b is wired up for ACE-lite, so (now that Panfrost knows
>>> how to handle this properly) we should describe it as such. Otherwise
>>> the mismatch leads to all manner of fun with mismatched attributes and
>>> inadvertently snooping stale data from caches, which would account for
>>> at least some of the brokenness observed on this platform.
>>>
>>> Signed-off-by: Robin Murphy <robin.murphy at arm.com>
>>> ---
>>>   arch/arm64/boot/dts/amlogic/meson-g12b.dtsi | 4 ++++
>>>   1 file changed, 4 insertions(+)
>>>
>>> diff --git a/arch/arm64/boot/dts/amlogic/meson-g12b.dtsi b/arch/arm64/boot/dts/amlogic/meson-g12b.dtsi
>>> index 9b8548e5f6e5..ee8fcae9f9f0 100644
>>> --- a/arch/arm64/boot/dts/amlogic/meson-g12b.dtsi
>>> +++ b/arch/arm64/boot/dts/amlogic/meson-g12b.dtsi
>>> @@ -135,3 +135,7 @@ map1 {
>>>   		};
>>>   	};
>>>   };
>>> +
>>> +&mali {
>>> +	dma-coherent;
>>> +};
>>>    
>>
>> Thanks a lot for digging, I'll run a test to confirm it fixes the issue !
> 
> Sorry for the late reply. I triggered a dEQP run with this patch applied
> and I see a bunch of "panfrost ffe40000.gpu: matching BO is not heap type"
> errors (see below for a full backtrace). That doesn't seem to happen when
> we drop this dma-coherent property.
> 
> [  690.945731] ------------[ cut here ]------------
> [  690.950003] panfrost ffe40000.gpu: matching BO is not heap type (GPU VA = 319a000)
> [  690.950051] WARNING: CPU: 0 PID: 120 at drivers/gpu/drm/panfrost/panfrost_mmu.c:465 panfrost_mmu_irq_handler_thread+0x47c/0x650
> [  690.968854] Modules linked in:
> [  690.971878] CPU: 0 PID: 120 Comm: irq/27-panfrost Tainted: G        W         5.9.0-rc5-02434-g7d8109ec5a42 #784
> [  690.981964] Hardware name: Khadas VIM3 (DT)
> [  690.986107] pstate: 60000005 (nZCv daif -PAN -UAO BTYPE=--)
> [  690.991627] pc : panfrost_mmu_irq_handler_thread+0x47c/0x650
> [  690.997232] lr : panfrost_mmu_irq_handler_thread+0x47c/0x650
> [  691.002836] sp : ffff800011bcbcd0
> [  691.006114] x29: ffff800011bcbcf0 x28: ffff0000f3fe3800
> [  691.011375] x27: ffff0000ceaf5350 x26: ffff0000ca5fc500
> [  691.016636] x25: ffff0000f32409c0 x24: 0000000000000001
> [  691.021897] x23: ffff0000f3240880 x22: ffff0000f3e3a800
> [  691.027159] x21: 0000000000000000 x20: 0000000000000000
> [  691.032420] x19: 0000000000010001 x18: 0000000000000020
> [  691.037681] x17: 0000000000000000 x16: 0000000000000000
> [  691.042942] x15: ffff0000f3fe3c70 x14: ffffffffffffffff
> [  691.048204] x13: ffff8000116c2428 x12: ffff8000116c2086
> [  691.053466] x11: ffff800011bcbcd0 x10: ffff800011bcbcd0
> [  691.058727] x9 : 00000000fffffffe x8 : 0000000000000000
> [  691.063988] x7 : 7420706165682074 x6 : ffff8000116c1816
> [  691.069249] x5 : 0000000000000000 x4 : 0000000000000000
> [  691.074510] x3 : 00000000ffffffff x2 : ffff8000e348c000
> [  691.079771] x1 : f1b91ff9af2df000 x0 : 0000000000000000
> [  691.085033] Call trace:
> [  691.087452]  panfrost_mmu_irq_handler_thread+0x47c/0x650
> [  691.092712]  irq_thread_fn+0x2c/0xa0
> [  691.096246]  irq_thread+0x184/0x208
> [  691.099699]  kthread+0x140/0x160
> [  691.102890]  ret_from_fork+0x10/0x34
> [  691.106424] ---[ end trace b5dd8c2dfada8236 ]---
> 

It's quite possible this is caused by the GPU seeing a stale page table 
entry, so perhaps coherency isn't working as well as it should...

Do you get an "Unhandled Page fault" message after this? It might give 
some clues. Coherency issues are a pain to debug though and it's of 
course possible there are issues on this specific platform.

Steve