Re: [RFC PATCH 0/3] spi/xilinx: Merge OF and non-OF drivers

[Michal Simek <monstr@monstr.eu>]

Hi, [cc: David Brownell]

Grant Likely wrote:
> On Mon, Nov 8, 2010 at 9:34 AM, John Linn <John.Linn@xilinx.com> wrote:
>>> -----Original Message-----
>>> From: Michal Simek [mailto:monstr@monstr.eu]
>>> Sent: Monday, November 08, 2010 6:29 AM
>>> To: grant.likely@secretlab.ca
>>> Cc: spi-devel-general@lists.sourceforge.net; richard.rojfors@mocean-labs.com; John Linn; linux-
>>> kernel@vger.kernel.org
>>> Subject: Re: [RFC PATCH 0/3] spi/xilinx: Merge OF and non-OF drivers
>>>
>>> Hi Grant,
>>>
>>> Grant Likely wrote:
>>>> Since of_platform_bus_type has been merged with the platform_bus_type,
>>>> a single platform driver can now support both use cases.  This patch
>>>> series merges the two halves of the xilinx_spi device driver.
>>>>
>>>> Compile tested only.  I haven't booted this yet.
>>> I have tested it on sp605 and works well. Have you added that patches
>>> to your repository? Or are they somewhere else? Who is responsible for?
>>>
>>> I would like to also discuss one change which is related mmc_spi kernel driver.
>>> Let me describe the problem. Microblaze can use dma in all addresses
>>> that's why dma_mask is setup to 0xffffffff in of_platform_device_create.
>>> Xilinx spi driver doesn't support dma but mmc_spi driver is checking dma_mask in parent device
>>> which is xilinx spi driver.
>>>
>>> Here is the corresponding the part of code (Expect dma_mask=zero for no dma operations).
>>> mmc_spi.c:~1395
>>>       if (spi->master->dev.parent->dma_mask) {
>>>               struct device   *dev = spi->master->dev.parent;
>>>
>>>               host->dma_dev = dev;
>>>
>>>
>>> Based on this one our customer came with the following solution to setup
>>> dma_mask in xilinx_spi to zero and then mmc_spi doesn't setup dma operation.
>>>
>>> I think that this is nice solution but I would like to be sure that I didn't miss anything.
>>> After that i will create proper patch with description.
>> Seems reasonable to me.
> 
> Hmmm, that actually is not sane.  Ideally, drivers should never be
> mucking with the dma mask.  It is supposed to only be set by the code
> actually registering the device.  The mmc code should not be looking
> at the parent's dma mask to determine if DMA is available; the spi bus
> drivers should be explicitly stating whether or not it supports DMA.
> The mmc_spi code is doing the wrong thing here.

I have no problem to fix mmc_spi driver but what is the standard way how to detect
DMA capability for this case? This part of code is in mmc_spi from the beginning that's why I am
wondering that none complain about.

David?

Sorry I don't have HW where I can test it. :-(

> 
> That being said, until the mmc_spi code is fixed (and all the users
> are fixed up so DMA still works) then this patch is probably the best
> solution.  However, please note that dev->dma_mask is a pointer, so
> you should actually be setting it to NULL.

Yes truth.

Michal



> 
> g.
> 
>> Thanks,
>> John
>>
>>>
>>> diff --git a/drivers/spi/xilinx_spi.c b/drivers/spi/xilinx_spi.c
>>> index 7adaef6..3612e1b 100644
>>> --- a/drivers/spi/xilinx_spi.c
>>> +++ b/drivers/spi/xilinx_spi.c
>>> @@ -519,6 +519,9 @@ static int __devinit xilinx_spi_probe(struct platform_device *dev)
>>>         }
>>>
>>>         platform_set_drvdata(dev, master);
>>> +       /* clear the dma_mask, to try to disable use of dma */
>>> +       dev->dev.dma_mask = 0;
>>> +
>>>         return 0;
>>>  }
>>>
>>>
>>> Thanks,
>>> Michal
>>>
>>>
>>> --
>>> Michal Simek, Ing. (M.Eng)
>>> w: www.monstr.eu p: +42-0-721842854
>>> Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
>>> Microblaze U-BOOT custodian
>>
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>>
> 
> 
> 


-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian