Re: [PATCH 4/4] iommu/arm-smmu: Use per-context TLB sync as appropriate

[Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>]

On 09/02/16 14:15, Will Deacon wrote:
> On Tue, Jan 26, 2016 at 06:06:37PM +0000, Robin Murphy wrote:
>> TLB synchronisation is a mighty big hammmer to bring down on the
>> transaction stream, typically stalling all in-flight transactions until
>> the sync completes. Since in most cases (except at stage 2 on SMMUv1)
>> a per-context sync operation is available, prefer that over the global
>> operation when performing TLB maintenance for a single domain, to avoid
>> unecessarily disrupting ongoing traffic in other contexts.
>>
>> Signed-off-by: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>
>> ---
>>   drivers/iommu/arm-smmu.c | 32 ++++++++++++++++++++++++--------
>>   1 file changed, 24 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>> index 18e0e10..bf1895c 100644
>> --- a/drivers/iommu/arm-smmu.c
>> +++ b/drivers/iommu/arm-smmu.c
>> @@ -219,6 +219,8 @@
>>   #define ARM_SMMU_CB_S1_TLBIVAL		0x620
>>   #define ARM_SMMU_CB_S2_TLBIIPAS2	0x630
>>   #define ARM_SMMU_CB_S2_TLBIIPAS2L	0x638
>> +#define ARM_SMMU_CB_TLBSYNC		0x7f0
>> +#define ARM_SMMU_CB_TLBSTATUS		0x7f4
>>   #define ARM_SMMU_CB_ATS1PR		0x800
>>   #define ARM_SMMU_CB_ATSR		0x8f0
>>
>> @@ -546,14 +548,22 @@ static void __arm_smmu_free_bitmap(unsigned long *map, int idx)
>>   }
>>
>>   /* Wait for any pending TLB invalidations to complete */
>> -static void __arm_smmu_tlb_sync(struct arm_smmu_device *smmu)
>> +static void __arm_smmu_tlb_sync(struct arm_smmu_device *smmu, int cbndx)
>>   {
>>   	int count = 0;
>> -	void __iomem *gr0_base = ARM_SMMU_GR0(smmu);
>> +	void __iomem *base, __iomem *status;
>>
>> -	writel_relaxed(0, gr0_base + ARM_SMMU_GR0_sTLBGSYNC);
>> -	while (readl_relaxed(gr0_base + ARM_SMMU_GR0_sTLBGSTATUS)
>> -	       & sTLBGSTATUS_GSACTIVE) {
>> +	if (cbndx < 0) {
>> +		base = ARM_SMMU_GR0(smmu);
>> +		status = base + ARM_SMMU_GR0_sTLBGSTATUS;
>> +		writel_relaxed(0, base + ARM_SMMU_GR0_sTLBGSYNC);
>> +	} else {
>> +		base = ARM_SMMU_CB_BASE(smmu) + ARM_SMMU_CB(smmu, cbndx);
>> +		status = base + ARM_SMMU_CB_TLBSTATUS;
>> +		writel_relaxed(0, base + ARM_SMMU_CB_TLBSYNC);
>> +	}
>> +
>> +	while (readl_relaxed(status) & sTLBGSTATUS_GSACTIVE) {
>>   		cpu_relax();
>>   		if (++count == TLB_LOOP_TIMEOUT) {
>>   			dev_err_ratelimited(smmu->dev,
>> @@ -567,7 +577,13 @@ static void __arm_smmu_tlb_sync(struct arm_smmu_device *smmu)
>>   static void arm_smmu_tlb_sync(void *cookie)
>>   {
>>   	struct arm_smmu_domain *smmu_domain = cookie;
>> -	__arm_smmu_tlb_sync(smmu_domain->smmu);
>> +	int cbndx = smmu_domain->cfg.cbndx;
>> +
>> +	if (smmu_domain->stage == ARM_SMMU_DOMAIN_S2 &&
>> +	    smmu_domain->smmu->version < ARM_SMMU_V2)
>> +		cbndx = -1;
>
> I think it would be cleaner just to override the sync function pointer
> when we initialise a stage-2 page table for an SMMUv1 implementation.
>
> Any reason not to go that way?

Frankly, the idea just didn't occur to me. Looking more closely, if we 
were to simply put a set of iommu_gather_ops pointers in each domain 
based on the format, we could then also break up the confusing mess of 
arm_smmu_tlb_inv_range_nosync(), which would be nice.

I'll give that a go on top of the context format series I'm preparing 
(with which it would otherwise conflict horribly) and see how it looks.

Robin.