linux-kernel - Re: [PATCH 3/3] iommu/arm-smmu: Error out only if not enough context interrupts

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Date:   Tue, 24 Jul 2018 15:09:41 +0530
From:   Vivek Gautam <vivek.gautam@...eaurora.org>
To:     Will Deacon <will.deacon@....com>
Cc:     joro@...tes.org, robh+dt@...nel.org, robin.murphy@....com,
        andy.gross@...aro.org, mark.rutland@....com,
        iommu@...ts.linux-foundation.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, tfiga@...omium.org,
        sricharan@...eaurora.org, linux-arm-msm@...r.kernel.org,
        david.brown@...aro.org, linux-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 3/3] iommu/arm-smmu: Error out only if not enough context
 interrupts

Hi Will,


On 7/24/2018 2:06 PM, Will Deacon wrote:
> On Thu, Jul 19, 2018 at 11:23:56PM +0530, Vivek Gautam wrote:
>> Currently we check if the number of context banks is not equal to
>> num_context_interrupts. However, there are booloaders such as, one
>> on sdm845 that reserves few context banks and thus kernel views
>> less than the total available context banks.
>> So, although the hardware definition in device tree would mention
>> the correct number of context interrupts, this number can be
>> greater than the number of context banks visible to smmu in kernel.
>> We should therefore error out only when the number of context banks
>> is greater than the available number of context interrupts.
>>
>> Signed-off-by: Vivek Gautam <vivek.gautam@...eaurora.org>
>> Suggested-by: Tomasz Figa <tfiga@...omium.org>
>> Cc: Robin Murphy <robin.murphy@....com>
>> Cc: Will Deacon <will.deacon@....com>
>> ---
>>   drivers/iommu/arm-smmu.c | 19 +++++++++++++------
>>   1 file changed, 13 insertions(+), 6 deletions(-)
>>
>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>> index 7c69736a30f8..4cb53bf4f423 100644
>> --- a/drivers/iommu/arm-smmu.c
>> +++ b/drivers/iommu/arm-smmu.c
>> @@ -2229,12 +2229,19 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
>>   	if (err)
>>   		return err;
>>   
>> -	if (smmu->version == ARM_SMMU_V2 &&
>> -	    smmu->num_context_banks != smmu->num_context_irqs) {
>> -		dev_err(dev,
>> -			"found only %d context interrupt(s) but %d required\n",
>> -			smmu->num_context_irqs, smmu->num_context_banks);
>> -		return -ENODEV;
>> +	if (smmu->version == ARM_SMMU_V2) {
>> +		if (smmu->num_context_banks > smmu->num_context_irqs) {
>> +			dev_err(dev,
>> +			      "found only %d context irq(s) but %d required\n",
>> +			      smmu->num_context_irqs, smmu->num_context_banks);
>> +			return -ENODEV;
>> +		} else if (smmu->num_context_banks < smmu->num_context_irqs) {
>> +			/* loose extra context interrupts */
>> +			dev_notice(dev,
>> +			      "found %d context irq(s) but only %d required\n",
>> +			      smmu->num_context_irqs, smmu->num_context_banks);
>> +			smmu->num_context_irqs = smmu->num_context_banks;
>> +		}
> I don't see the utility in the new message. Can you simplify with the patch
> below on top? It's a bit weird that we only decide to ignore the extra irqs
> after calling platform_get_irq() on them, but that seems to be harmless.

Thanks. I will modify as suggested below and respin.

Best regards
Vivek

>
> Will
>
> --->8
>
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index aa46c1ed5bf9..5349e22b5c78 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -2109,13 +2109,10 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
>   			      "found only %d context irq(s) but %d required\n",
>   			      smmu->num_context_irqs, smmu->num_context_banks);
>   			return -ENODEV;
> -		} else if (smmu->num_context_banks < smmu->num_context_irqs) {
> -			/* loose extra context interrupts */
> -			dev_notice(dev,
> -			      "found %d context irq(s) but only %d required\n",
> -			      smmu->num_context_irqs, smmu->num_context_banks);
> -			smmu->num_context_irqs = smmu->num_context_banks;
>   		}
> +
> +		/* Ignore superfluous interrupts */
> +		smmu->num_context_irqs = smmu->num_context_banks;
>   	}
>   
>   	for (i = 0; i < smmu->num_global_irqs; ++i) {
> --
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