linux-kernel - Re: [RFC PATCH V2] scsi: ufs: Add specific callback for setting DMA mask

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Date:   Wed, 16 May 2018 14:31:06 -0700
From:   Subhash Jadavani <subhashj@...eaurora.org>
To:     Alim Akhtar <alim.akhtar@...il.com>
Cc:     Alim Akhtar <alim.akhtar@...sung.com>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, jejb@...ux.vnet.ibm.com,
        martin.petersen@...cle.com,
        vinayak holikatti <vinholikatti@...il.com>,
        devicetree@...r.kernel.org,
        Shaik Ameer Basha <shaik.ameer@...sung.com>
Subject: Re: [RFC PATCH V2] scsi: ufs: Add specific callback for setting DMA
 mask

On 2018-05-15 21:31, Alim Akhtar wrote:
> Ping !!!
> 
> On Thu, Mar 8, 2018 at 4:33 PM, Alim Akhtar <alim.akhtar@...sung.com> 
> wrote:
>> Currently DMA mask for UFS HCI is set by reading CAP register's
>> [64AS] bit. Some HCI controller like Exynos support 36-bit bus 
>> address.
>> This works perfectly fine with DMA mask set as 64 in case there is no
>> IOMMU attached to HCI.
>> In case if HCI is behind an IOMMU, setting DMA mask as 64 bit won't
>> work as HCI has only 36bit addressing and SMMU has created mapping of
>> 64 bit and as the device truncates the address, its mapping will not
>> be found by iommu.
>> To resolve such issues, let the variant driver sets its own DMA mask.
>> 
>> Signed-off-by: Alim Akhtar <alim.akhtar@...sung.com>
>> ---
>>  drivers/scsi/ufs/ufshcd.c | 3 +++
>>  drivers/scsi/ufs/ufshcd.h | 2 ++
>>  2 files changed, 5 insertions(+)
>> 
>> I am not sure if there are other ways available to handle such cases.
>> The IOMMU I am talking about is arm-smmu and it DT binding does not
>> give much idea about handling such cases.
>> Have tested this patch with HCI controller with IOMMU attached.
>> 
>> Changes Since V1:
>>         - Fixed build issue as reported by Kbuild test robot.
>> 
>> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
>> index a355d98..9a1374e 100644
>> --- a/drivers/scsi/ufs/ufshcd.c
>> +++ b/drivers/scsi/ufs/ufshcd.c
>> @@ -7781,6 +7781,9 @@ EXPORT_SYMBOL_GPL(ufshcd_dealloc_host);
>>   */
>>  static int ufshcd_set_dma_mask(struct ufs_hba *hba)
>>  {
>> +       if (hba->vops && hba->vops->set_dma_mask)
>> +               return hba->vops->set_dma_mask(hba);
>> +
>>         if (hba->capabilities & MASK_64_ADDRESSING_SUPPORT) {
>>                 if (!dma_set_mask_and_coherent(hba->dev, 
>> DMA_BIT_MASK(64)))
>>                         return 0;
>> diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
>> index 1332e54..89c6dae 100644
>> --- a/drivers/scsi/ufs/ufshcd.h
>> +++ b/drivers/scsi/ufs/ufshcd.h
>> @@ -297,6 +297,7 @@ struct ufs_pwr_mode_info {
>>   * @resume: called during host controller PM callback
>>   * @dbg_register_dump: used to dump controller debug information
>>   * @phy_initialization: used to initialize phys
>> + * @set_dma_mask: used to set variant specific DMA mask
>>   */
>>  struct ufs_hba_variant_ops {
>>         const char *name;
>> @@ -325,6 +326,7 @@ struct ufs_hba_variant_ops {
>>         int     (*resume)(struct ufs_hba *, enum ufs_pm_op);
>>         void    (*dbg_register_dump)(struct ufs_hba *hba);
>>         int     (*phy_initialization)(struct ufs_hba *);
>> +       int     (*set_dma_mask)(struct ufs_hba *hba);
>>  };
>> 
>>  /* clock gating state  */
>> --
>> 2.7.4
>> 

Looks reasonable to me, you may try posting non-RFC version.

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