linux-kernel - Re: [PATCH V3] scsi: ufs: Add specific callback for setting DMA mask

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Date:   Sun, 20 May 2018 07:50:32 +0530
From:   Alim Akhtar <alim.akhtar@...sung.com>
To:     linux-scsi@...r.kernel.o, linux-kernel@...r.kernel.org
Cc:     jejb@...ux.vnet.ibm.com, martin.petersen@...cle.com,
        subhashj@...eaurora.org, vinholikatti@...il.com,
        shaik.ameer@...sung.com
Subject: Re: [PATCH V3] scsi: ufs: Add specific callback for setting DMA
 mask

Hi All
Please ignore the below patch, sorry for the noise.
Will send updated patch soon.

Regards,
Alim

On 05/20/2018 07:41 AM, Bharat Uppal wrote:
> From: Alim Akhtar <alim.akhtar@...sung.com>
> 
> 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.
> 
> Changes Since V2:
> 	- Remove RFC tag as suggested by Subhash.
> 
> 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  */
>