Re: [PATCH 1/2] ufs-pltfrm: initialize DMA mask for device-tree probed device

["Akinobu Mita" <mita@fixstars.com>]

> On 8/19/2013 8:02 PM, James Bottomley wrote:
>> On Mon, 2013-08-19 at 22:56 +0900, Akinobu Mita wrote:
>>> The device-tree probed device for ARM doesn't have dev->dma_mask.
>>> So dma_set_mask() for the device doesn't succeed.  The popular trick
>>> for this is - dev->dma_mask = &dev->coherent_dma_mask;
>>>
>>> Currently there is no dma_set_mask() call in ufs-pltfrm, but the
>>> forthcoming fix needs proper DMA mask setting in ufs core driver.  So
>>> initializing dev->dma_mask as described above is required.
>>>
>>> Signed-off-by: Akinobu Mita <mita@fixstars.com>
>>> Cc: Sujit Reddy Thumma <sthumma@codeaurora.org>
>>> Cc: Vinayak Holikatti <vinholikatti@gmail.com>
>>> Cc: Santosh Y <santoshsy@gmail.com>
>>> Cc: "James E.J. Bottomley" <JBottomley@parallels.com>
>>> Cc: linux-scsi@vger.kernel.org
>>> ---
>>>   drivers/scsi/ufs/ufshcd-pltfrm.c | 3 +++
>>>   1 file changed, 3 insertions(+)
>>>
>>> diff --git a/drivers/scsi/ufs/ufshcd-pltfrm.c
>>> b/drivers/scsi/ufs/ufshcd-pltfrm.c
>>> index 94ba40c..c780840 100644
>>> --- a/drivers/scsi/ufs/ufshcd-pltfrm.c
>>> +++ b/drivers/scsi/ufs/ufshcd-pltfrm.c
>>> @@ -122,6 +122,9 @@ static int ufshcd_pltfrm_probe(struct
>>> platform_device *pdev)
>>>   goto out;
>>>   }
>>>
>>> +if (!dev->dma_mask)
>>> +dev->dma_mask = &dev->coherent_dma_mask;
>>> +
>>
>> If the DMA mask is NULL, it means there's buggy platform code somewhere;
>> I'm not sure we should be hacking a fix in a SCSI driver.
>
> Yes, ideally DT core should do this, there are patches lying around but
> are not converged. Adding devicetree@vger.kernel.org to see if someone
> has better suggestions.
>
> Recent additions to kernel with similar hacks -
> https://patchwork.kernel.org/patch/2537021/

The discussion in that thread is useful.  Also, I found that Russell King
proposed replacing the boilerplate by using dma_coerce_mask_and_coherent()
in his patch set "Preview of DMA mask changes".
https://patchwork.kernel.org/patch/2837359/