Date:   Mon, 8 Apr 2019 09:56:05 +0100
From:   Steven Price <steven.price@....com>
To:     Robin Murphy <robin.murphy@....com>, Rob Herring <robh@...nel.org>,
        dri-devel@...ts.freedesktop.org
Cc:     Neil Armstrong <narmstrong@...libre.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, David Airlie <airlied@...ux.ie>,
        iommu@...ts.linux-foundation.org,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Sean Paul <sean@...rly.run>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 1/3] iommu: io-pgtable: Add ARM Mali midgard MMU page
 table format

On 05/04/2019 11:36, Steven Price wrote:
> On 05/04/2019 10:51, Robin Murphy wrote:
>> Hi Steve,
>>
>> On 05/04/2019 10:42, Steven Price wrote:
>>> First let me say congratulations to everyone working on Panfrost - it's
>>> an impressive achievement!
>>>
>>> Full disclosure: I used to work on the Mali kbase driver. And have been
>>> playing around with running the Mali user-space blob with the Panfrost
>>> kernel driver.
>>>
>>> On 01/04/2019 08:47, Rob Herring wrote:
>>>> ARM Mali midgard GPU is similar to standard 64-bit stage 1 page
>>>> tables, but
>>>> have a few differences. Add a new format type to represent the
>>>> format. The
>>>> input address size is 48-bits and the output address size is 40-bits
>>>> (and
>>>> possibly less?). Note that the later bifrost GPUs follow the standard
>>>> 64-bit stage 1 format.
>>>>
>>>> The differences in the format compared to 64-bit stage 1 format are:
>>>>
>>>> The 3rd level page entry bits are 0x1 instead of 0x3 for page entries.
>>>>
>>>> The access flags are not read-only and unprivileged, but read and write.
>>>> This is similar to stage 2 entries, but the memory attributes field
>>>> matches
>>>> stage 1 being an index.
>>>>
>>>> The nG bit is not set by the vendor driver. This one didn't seem to
>>>> matter,
>>>> but we'll keep it aligned to the vendor driver.
>>>
>>> The nG bit should be ignored by the hardware.
>>>
>>> The MMU in Midgard/Bifrost has a quirk similar to
>>> IO_PGTABLE_QUIRK_TLBI_ON_MAP - you must perform a cache flush for the
>>> GPU to (reliably) pick up new page table mappings.
>>>
>>> You may not have seen this because of the use of the JS_CONFIG_START_MMU
>>> bit - this effectively performs a cache flush and TLB invalidate before
>>> starting a job, however when using a GPU like T760 (e.g. on the Firefly
>>> RK3288) this bit isn't being set. In my testing on the Firefly board I
>>> saw GPU page faults because of this.
>>>
>>> There's two options for fixing this - a patch like below adds the quirk
>>> mode to the MMU. Or alternatively always set JS_CONFIG_START_MMU on
>>> jobs. In my testing both options solve the page faults.
>>>
>>> To be honest I don't know the reasoning behind kbase making the
>>> JS_CONFIG_START_MMU bit conditional - I'm not aware of any reason why it
>>> can't always be set. My guess is performance, but I haven't benchmarked
>>> the difference between this and JS_CONFIG_START_MMU.
>>>
>>> -----8<----------
>>>  From e3f75c7f04e43238dfc579029b8c11fb6b4a0c18 Mon Sep 17 00:00:00 2001
>>> From: Steven Price <steven.price@....com>
>>> Date: Thu, 4 Apr 2019 15:53:17 +0100
>>> Subject: [PATCH] iommu: io-pgtable: IO_PGTABLE_QUIRK_TLBI_ON_MAP for LPAE
>>>
>>> Midgard/Bifrost GPUs require a TLB invalidation when mapping pages,
>>> implement IO_PGTABLE_QUIRK_TLBI_ON_MAP for LPAE iommu page table
>>> formats and add the quirk bit to Panfrost.
>>>
>>> Signed-off-by: Steven Price <steven.price@....com>
>>> ---
>>>   drivers/gpu/drm/panfrost/panfrost_mmu.c |  1 +
>>>   drivers/iommu/io-pgtable-arm.c          | 11 +++++++++--
>>>   2 files changed, 10 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/panfrost/panfrost_mmu.c
>>> b/drivers/gpu/drm/panfrost/panfrost_mmu.c
>>> index f3aad8591cf4..094312074d66 100644
>>> --- a/drivers/gpu/drm/panfrost/panfrost_mmu.c
>>> +++ b/drivers/gpu/drm/panfrost/panfrost_mmu.c
>>> @@ -343,6 +343,7 @@ int panfrost_mmu_init(struct panfrost_device *pfdev)
>>>       mmu_write(pfdev, MMU_INT_MASK, ~0);
>>>
>>>       pfdev->mmu->pgtbl_cfg = (struct io_pgtable_cfg) {
>>> +        .quirks        = IO_PGTABLE_QUIRK_TLBI_ON_MAP,
>>>           .pgsize_bitmap    = SZ_4K, // | SZ_2M | SZ_1G),
>>>           .ias        = 48,
>>>           .oas        = 40,    /* Should come from dma mask? */
>>> diff --git a/drivers/iommu/io-pgtable-arm.c
>>> b/drivers/iommu/io-pgtable-arm.c
>>> index 84beea1f47a7..45fd7bbdf9aa 100644
>>> --- a/drivers/iommu/io-pgtable-arm.c
>>> +++ b/drivers/iommu/io-pgtable-arm.c
>>> @@ -505,7 +505,13 @@ static int arm_lpae_map(struct io_pgtable_ops *ops,
>>> unsigned long iova,
>>>        * Synchronise all PTE updates for the new mapping before there's
>>>        * a chance for anything to kick off a table walk for the new iova.
>>>        */
>>> -    wmb();
>>> +    if (data->iop.cfg.quirks & IO_PGTABLE_QUIRK_TLBI_ON_MAP) {
>>> +        io_pgtable_tlb_add_flush(&data->iop, iova, size,
>>> +                     ARM_LPAE_BLOCK_SIZE(2, data), false);
>>
>> For correctness (in case this ever ends up used for something with
>> VMSA-like invalidation behaviour), the granule would need to be "size"
>> here, rather than effectively hard-coded.
> 
> Ah yes - I did rather just copy/paste this from io-pgtable-arm-v7s with
> minor fix-ups.
> 
>> However, since Mali's invalidations appear to operate on arbitrary
>> ranges, it would probably be a lot more efficient for the driver to
>> handle this case directly, by just issuing a single big invalidation
>> after the for_each_sg() loop in panfrost_mmu_map().
> 
> Yes - that would probably be a better option. Although I think
> personally I'd lean towards just using JS_CONFIG_START_MMU for most
> cases. The only thing that won't handle is modifying the MMU while the
> job is running (e.g. faulting in pages). But that can be handled
> internally in Panfrost by invalidating the exact region which is being
> populated.

I asked around. Apparently there are some interesting issues with
START_MMU on some hardware revisions. So best to follow mali_kbase here
and only use START_MMU on those hardware revisions that mali_kbase does
(what Panfrost is already doing). Which means we'll definitely need this
quirk in some form.

Steve

> 
> Steve
> 
>> Robin.
>>
>>> +        io_pgtable_tlb_sync(&data->iop);
>>> +    } else {
>>> +        wmb();
>>> +    }
>>>
>>>       return ret;
>>>   }
>>> @@ -800,7 +806,8 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg
>>> *cfg, void *cookie)
>>>       struct arm_lpae_io_pgtable *data;
>>>
>>>       if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS |
>>> IO_PGTABLE_QUIRK_NO_DMA |
>>> -                IO_PGTABLE_QUIRK_NON_STRICT))
>>> +                IO_PGTABLE_QUIRK_NON_STRICT |
>>> +                IO_PGTABLE_QUIRK_TLBI_ON_MAP))
>>>           return NULL;
>>>
>>>       data = arm_lpae_alloc_pgtable(cfg);
>>>
>> _______________________________________________
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>> dri-devel@...ts.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> 
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