linux-kernel - Re: [PATCH] scsi: ufs: core: Limit DMA alignment check

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Message-ID: <20230201102748.GA62808@thinkpad>
Date:   Wed, 1 Feb 2023 15:57:48 +0530
From:   Manivannan Sadhasivam <mani@...nel.org>
To:     Bjorn Andersson <quic_bjorande@...cinc.com>
Cc:     Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        Bart Van Assche <bvanassche@....org>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Asutosh Das <quic_asutoshd@...cinc.com>,
        Bean Huo <beanhuo@...ron.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Jinyoung Choi <j-young.choi@...sung.com>,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] scsi: ufs: core: Limit DMA alignment check

On Tue, Jan 31, 2023 at 07:49:17PM -0800, Bjorn Andersson wrote:
> The three DMA memory regions allocated for the host memory space is
> documented to require alignment of 128, 1024 and 1024 respectively, but
> the returned address is checked for PAGE_SIZE alignment.
> 
> In the case these allocations are serviced by e.g. the Arm SMMU, the
> size and alignment will be determined by its supported page sizes. In
> most cases SZ_4K and a few larger sizes are available.
> 
> In the typical configuration this does not cause problems, but in the
> event that the system PAGE_SIZE is increased beyond 4k, it's no longer
> reasonable to expect that the allocation will be PAGE_SIZE aligned.
> 
> Limit the DMA alignment check to the actual alignment requirements
> written in the comments in the code, to avoid the UFS core refusing to
> initialize with such configuration.

Isn't dma_alloc_coherent() supposed to return PAGE_SIZE aligned dma and cpu
addresses? I suppose that could be reason for checking against PAGE_SIZE.

> 
> Signed-off-by: Bjorn Andersson <quic_bjorande@...cinc.com>

But it doesn't hurt to check for the actual alignment.

Reviewed-by: Manivannan Sadhasivam <mani@...nel.org>

Thanks,
Mani

> ---
>  drivers/ufs/core/ufshcd.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
> index ec732e4bbbf4..d7f3f1ba9d12 100644
> --- a/drivers/ufs/core/ufshcd.c
> +++ b/drivers/ufs/core/ufshcd.c
> @@ -3724,12 +3724,9 @@ static int ufshcd_memory_alloc(struct ufs_hba *hba)
>  
>  	/*
>  	 * UFSHCI requires UTP command descriptor to be 128 byte aligned.
> -	 * make sure hba->ucdl_dma_addr is aligned to PAGE_SIZE
> -	 * if hba->ucdl_dma_addr is aligned to PAGE_SIZE, then it will
> -	 * be aligned to 128 bytes as well
>  	 */
>  	if (!hba->ucdl_base_addr ||
> -	    WARN_ON(hba->ucdl_dma_addr & (PAGE_SIZE - 1))) {
> +	    WARN_ON(hba->ucdl_dma_addr & (128 - 1))) {
>  		dev_err(hba->dev,
>  			"Command Descriptor Memory allocation failed\n");
>  		goto out;
> @@ -3745,7 +3742,7 @@ static int ufshcd_memory_alloc(struct ufs_hba *hba)
>  						   &hba->utrdl_dma_addr,
>  						   GFP_KERNEL);
>  	if (!hba->utrdl_base_addr ||
> -	    WARN_ON(hba->utrdl_dma_addr & (PAGE_SIZE - 1))) {
> +	    WARN_ON(hba->utrdl_dma_addr & (1024 - 1))) {
>  		dev_err(hba->dev,
>  			"Transfer Descriptor Memory allocation failed\n");
>  		goto out;
> @@ -3769,7 +3766,7 @@ static int ufshcd_memory_alloc(struct ufs_hba *hba)
>  						    &hba->utmrdl_dma_addr,
>  						    GFP_KERNEL);
>  	if (!hba->utmrdl_base_addr ||
> -	    WARN_ON(hba->utmrdl_dma_addr & (PAGE_SIZE - 1))) {
> +	    WARN_ON(hba->utmrdl_dma_addr & (1024 - 1))) {
>  		dev_err(hba->dev,
>  		"Task Management Descriptor Memory allocation failed\n");
>  		goto out;
> -- 
> 2.25.1
> 

-- 
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