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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4CD8F884.30409@monstr.eu>
Date:	Tue, 09 Nov 2010 08:30:12 +0100
From:	Michal Simek <monstr@...str.eu>
To:	Grant Likely <grant.likely@...retlab.ca>
CC:	John Linn <John.Linn@...inx.com>,
	spi-devel-general@...ts.sourceforge.net,
	richard.rojfors@...ean-labs.com, linux-kernel@...r.kernel.org,
	dbrownell@...rs.sourceforge.net
Subject: Re: [RFC PATCH 0/3] spi/xilinx: Merge OF and non-OF drivers

Hi, [cc: David Brownell]

Grant Likely wrote:
> On Mon, Nov 8, 2010 at 9:34 AM, John Linn <John.Linn@...inx.com> wrote:
>>> -----Original Message-----
>>> From: Michal Simek [mailto:monstr@...str.eu]
>>> Sent: Monday, November 08, 2010 6:29 AM
>>> To: grant.likely@...retlab.ca
>>> Cc: spi-devel-general@...ts.sourceforge.net; richard.rojfors@...ean-labs.com; John Linn; linux-
>>> kernel@...r.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
>>
>> This email and any attachments are intended for the sole use of the named recipient(s) and contain(s) confidential information that may be proprietary, privileged or copyrighted under applicable law. If you are not the intended recipient, do not read, copy, or forward this email message or any attachments. Delete this email message and any attachments immediately.
>>
> 
> 
> 


-- 
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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/