Potential issue with SDHCI DMA

[adrian.hunter@intel.com (Adrian Hunter)]

+ linux-mmc

On 29/04/16 11:58, Adrian Hunter wrote:
> On 18/04/16 17:33, Arnd Bergmann wrote:
>> On Monday 18 April 2016 09:58:04 Adrian Hunter wrote:
>>>
>>> Thanks for looking.
>>>
>>> It looked to me like sdhci-pxav3 devices created by mmp2_add_sdhost() might
>>> also be candidates.
>>>
>>
>> Oh, you are right, I missed that.
>>
>> I remember looking at sdhci-pxav2 and not finding any machine defining one,
>> but I must have skipped over sdhci-pxav3 failing to realize that this is
>> a different one.
>>
>> 	Arnd
>>
> 
> OK, so my plan to email sdhci driver maintainers ran into a snag.  It turned
> out to be too hard to dig up email addresses.  I have grabbed a few names
> and cc'ed them to this email anyway.
> 
> For those people, the issue is this:
> 
> An unexpected side-effect of commit 7b91369b4655 ("mmc: sdhci: Set DMA mask
> when adding host") is that SDHCI devices that do not define a DMA mask may
> find that DMA no longer works.  That was the case for a sdhci-esdhc-imx
> device, but that has been fixed - refer commit fc26fe9c3869 ("ARM: mach-imx:
> sdhci-esdhc-imx: initialize DMA mask").
> 
> DeviceTree, ACPI and PCI always set up a DMA mask for devices that they
> enumerate, so only hard-coded platform devices are expected to be affected.
> 
> We found only one other candidate: sdhci-pxav3 devices created by
> mmp2_add_sdhost().  Not sure if anyone has looked at that though.
> 
> Obviously, if you are unsure if your devices are affected, you can test and
> if there is a problem you will see the warning messages "mmcX: Failed to set
> 32-bit DMA mask" and "mmcX: No suitable DMA available - falling back to PIO".
> 
> Regards
> Adrian
> 
>