linux-kernel - Re: [PATCH 1/2] iommu/vt-d: Remove the dead code in init_iommu

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Date:   Wed, 31 May 2023 14:55:23 +0800
From:   Yanfei Xu <yanfei.xu@...el.com>
To:     Baolu Lu <baolu.lu@...ux.intel.com>, <dwmw2@...radead.org>,
        <joro@...tes.org>, <will@...nel.org>, <robin.murphy@....com>
CC:     <iommu@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] iommu/vt-d: Remove the dead code in init_iommu_hw()

Hi Baolu,

On 5/31/2023 11:24 AM, Baolu Lu wrote:
> On 5/30/23 5:25 PM, Yanfei Xu wrote:
>> After 'commit 2a41ccee2fdc ("iommu/vt-d: Change
>> iommu_enable/disable_translation to return void")', init_iommu_hw() only
>> returns 0. If statement for return value of this function is 
>> meaningless.
>> Hence change init_iommu_hw() to return viod and remove the dead code of
>> if statement in init_iommu_hw()
>>
>> Signed-off-by: Yanfei Xu<yanfei.xu@...el.com>
>> ---
>>   drivers/iommu/intel/iommu.c | 12 ++----------
>>   1 file changed, 2 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>> index 8096273b034c..e98f1b122b49 100644
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -2963,7 +2963,7 @@ static void __init init_no_remapping_devices(void)
>>   }
>>     #ifdef CONFIG_SUSPEND
>> -static int init_iommu_hw(void)
>> +static void init_iommu_hw(void)
>>   {
>>       struct dmar_drhd_unit *drhd;
>>       struct intel_iommu *iommu = NULL;
>> @@ -2988,8 +2988,6 @@ static int init_iommu_hw(void)
>>           iommu_enable_translation(iommu);
>>           iommu_disable_protect_mem_regions(iommu);
>>       }
>> -
>> -    return 0;
>
> 2966 static int init_iommu_hw(void)
> 2967 {
> 2968         struct dmar_drhd_unit *drhd;
> 2969         struct intel_iommu *iommu = NULL;
> 2970
> 2971         for_each_active_iommu(iommu, drhd)
> 2972                 if (iommu->qi)
> 2973                         dmar_reenable_qi(iommu);
>
> dmar_reenable_qi() still possibly returns an error number. It's better
> to pass this error number to the caller of init_iommu_hw()?
>
Event dmar_reenable_qi can return error number, but there is no caller
check it. As below, only these two places invoke it:
1. init_iommu_hw->dmar_reenable_qi
2. reenable_irq_remapping->dmar_reenable_qi

I think we can also convert dmar_reenable_qi() to return void:
diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
index a3414afe11b0..1432483c79e8 100644
--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -2112,13 +2112,10 @@ int __init enable_drhd_fault_handling(void)
  /*
   * Re-enable Queued Invalidation interface.
   */
-int dmar_reenable_qi(struct intel_iommu *iommu)
+void dmar_reenable_qi(struct intel_iommu *iommu)
  {
-       if (!ecap_qis(iommu->ecap))
-               return -ENOENT;
-
-       if (!iommu->qi)
-               return -ENOENT;
+       WARN_ON(!iommu->qi || !ecap_qis(iommu->ecap))
+               return;

         /*
          * First disable queued invalidation.
@@ -2130,8 +2127,6 @@ int dmar_reenable_qi(struct intel_iommu *iommu)
          * invalidation.
          */
         __dmar_enable_qi(iommu);
-
-       return 0;
  }

 From my understanding, dmar_reenable_qi() is used in suspend/resume case,
so the extended cap of an existing IOMMU hardware is unlikely changed. As
for the check of iommu->qi, if dmar_reenable_qi() can be invoked all is
depended on the no-NULL of iommu->qi at first. How about using WARN_ON for
both of them to simply this function.

Thanks,
Yanfei

> 2974
> 2975         for_each_iommu(iommu, drhd) {
> 2976                 if (drhd->ignored) {
>
> Best regards,
> baolu