linux-kernel - Re: [PATCHv7 1/7] iommu/io-pgtable-arm: Add support to use system cache

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Date:   Wed, 11 Nov 2020 11:32:42 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Will Deacon <will@...nel.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Rob Clark <robdclark@...il.com>,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        freedreno@...ts.freedesktop.org,
        "Kristian H . Kristensen" <hoegsberg@...gle.com>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCHv7 1/7] iommu/io-pgtable-arm: Add support to use system
 cache

On 2020-11-10 17:48, Will Deacon wrote:
> On Fri, Oct 30, 2020 at 02:53:08PM +0530, Sai Prakash Ranjan wrote:
>> Add a quirk IO_PGTABLE_QUIRK_SYS_CACHE to override the
>> attributes set in TCR for the page table walker when
>> using system cache.
>> 
>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
>> ---
>>  drivers/iommu/io-pgtable-arm.c | 7 ++++++-
>>  include/linux/io-pgtable.h     | 4 ++++
>>  2 files changed, 10 insertions(+), 1 deletion(-)
>> 
>> diff --git a/drivers/iommu/io-pgtable-arm.c 
>> b/drivers/iommu/io-pgtable-arm.c
>> index a7a9bc08dcd1..a356caf1683a 100644
>> --- a/drivers/iommu/io-pgtable-arm.c
>> +++ b/drivers/iommu/io-pgtable-arm.c
>> @@ -761,7 +761,8 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg 
>> *cfg, void *cookie)
>> 
>>  	if (cfg->quirks & ~(IO_PGTABLE_QUIRK_ARM_NS |
>>  			    IO_PGTABLE_QUIRK_NON_STRICT |
>> -			    IO_PGTABLE_QUIRK_ARM_TTBR1))
>> +			    IO_PGTABLE_QUIRK_ARM_TTBR1 |
>> +			    IO_PGTABLE_QUIRK_SYS_CACHE))
>>  		return NULL;
>> 
>>  	data = arm_lpae_alloc_pgtable(cfg);
>> @@ -773,6 +774,10 @@ arm_64_lpae_alloc_pgtable_s1(struct 
>> io_pgtable_cfg *cfg, void *cookie)
>>  		tcr->sh = ARM_LPAE_TCR_SH_IS;
>>  		tcr->irgn = ARM_LPAE_TCR_RGN_WBWA;
>>  		tcr->orgn = ARM_LPAE_TCR_RGN_WBWA;
>> +	} else if (cfg->quirks & IO_PGTABLE_QUIRK_SYS_CACHE) {
>> +		tcr->sh = ARM_LPAE_TCR_SH_OS;
>> +		tcr->irgn = ARM_LPAE_TCR_RGN_NC;
>> +		tcr->orgn = ARM_LPAE_TCR_RGN_WBWA;
> 
> Given that this only applies in the case where then page-table walker 
> is
> non-coherent, I think we'd be better off renaming the quirk to 
> something
> like IO_PGTABLE_QUIRK_ARM_OUTER_WBWA and then rejecting it in the
> non-coherent case.
> 

Do you mean like below?

diff --git a/drivers/iommu/io-pgtable-arm.c 
b/drivers/iommu/io-pgtable-arm.c
index a7a9bc08dcd1..94de1f71db42 100644
--- a/drivers/iommu/io-pgtable-arm.c
+++ b/drivers/iommu/io-pgtable-arm.c
@@ -776,7 +776,10 @@ arm_64_lpae_alloc_pgtable_s1(struct io_pgtable_cfg 
*cfg, void *cookie)
         } else {
                 tcr->sh = ARM_LPAE_TCR_SH_OS;
                 tcr->irgn = ARM_LPAE_TCR_RGN_NC;
-               tcr->orgn = ARM_LPAE_TCR_RGN_NC;
+               if (!(cfg->quirks & IO_PGTABLE_QUIRK_ARM_OUTER_WBWA))
+                       tcr->orgn = ARM_LPAE_TCR_RGN_NC;
+               else
+                       tcr->orgn = ARM_LPAE_TCR_RGN_WBWA;
         }

         tg1 = cfg->quirks & IO_PGTABLE_QUIRK_ARM_TTBR1;


Thanks,
Sai

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