Re: [PATCH RFC 0/2] ARM: shmobile: lager: Enable DMA bounce for PCI

[Ben Dooks <ben.dooks@codethink.co.uk>]

On 29/01/14 16:37, Valentine wrote:
> On 01/29/2014 08:03 PM, Ben Dooks wrote:
>> On 29/01/14 12:47, Valentine wrote:
>>> On 01/29/2014 04:45 PM, Ben Dooks wrote:
>>>> On 29/01/14 11:15, Valentine wrote:
>>>>> On 01/29/2014 12:03 PM, Ben Dooks wrote:
>>>>>> On 29/01/14 06:45, Simon Horman wrote:
>>>>>>> On Tue, Jan 28, 2014 at 10:53:31PM +0400, Valentine Barshak wrote:
>>>>>>>> This enables DMA bounce for PCI since the controller does
>>>>>>>> not support more than 2G PCI-AHB memory window.
>>>>>>>> The problems with DMA transfers can be observed when
>>>>>>>> setting 2G/2G user/kernel memory split model
>>>>>>>> (CONFIG_VMSPLIT_2G=y)
>>>>>>>> These patches help to avoid it.
>>>>>>>
>>>>>>> Are these patches compatible with other user/kernel splits?
>>>>>>
>>>>>> PS, the bridge is only actually capable of seeing 1GiB of
>>>>>> RAM due to alignment issues in the window. You can have either
>>>>>> 0x4..0x8 or 0x8..0xc but not /both/. If you open the window to
>>>>>> 2GiB then you can see either 0x0..0x8 or 0x8..0xF range.
>>>>>>
>>>>>
>>>>> I don't think this is relater to the user/kernel space memory split.
>>>>>
>>>>> Currently the R-Car Gen2 PCI driver uses 0x40000000 - 0x7fffffff
>>>>> PCI-AHB region. We can set it to 0x00000000 - 0x7fffffff,
>>>>> but there's no RAM below 0x40000000 so no DMA access to that area is
>>>>> actually legal from the PCI USB host driver.
>>>>> So the change wouldn't give us much.
>>>>
>>>> Well, there's IO areas but probably not wanting to DMA to them anyway.
>>>>
>>>>> The 31-bit DMA mask takes care of forbidding any DMA transfers
>>>>> to the area above 0x7fffffff.
>>>>
>>>> I will add this to our current patch series and see if it helps.
>>>
>>> Helps with what?
>>>
>>> I don't see any issues with the current patches.
>>
>> We're clearly not testing the same configurations, as all your patches
>> either are not DT enabled or are for the non-multiplatform kernel
>> builds. I've tried porting your DMA bounce changes to the
>> multiplatform board-lager-reference.c file but that has not fixed
>> the issue for me.
>
> Yes, my patches are not for the DT support. They have been around for quite
> a while and my goal is to have them applied first and add DT later.
>
> You've probably done something wrong while trying to support multiplatform.
> It looks like you're either missing the patches mentioned here:
> http://marc.info/?l=linux-sh&m\x139060253506760&w=2
> or you're not binding the PCI devices to the USB phy.
> Do you have USB R-Car Gen2 phy driver enabled?
> I don't see ehci/ochi probe being deferred until USB phy is ready.
> That's why you see this error.
>
> Please, discard your own follow the steps from the link above.
> I think you mentioned lately that you had tried the non-multiplatform
> version
> and it had not worked for you. Did you actually try it?
>
> Thanks,
> Val.

I have a local patch that forces the PHY on as soon as it gets
probed by the device tree because I have not had the time to sort
out the link between the DT and the PCI.

> $ grep GEN2 out/test/.config
> CONFIG_PCI_RCAR_GEN2=y
> # CONFIG_PCI_RCAR_GEN2_ERRIRQ is not set
> CONFIG_USB_RCAR_GEN2_PHY=y

I /will/ go and check the driver is actually being probed in
case there is an issue there.

-- 
Ben Dooks				http://www.codethink.co.uk/
Senior Engineer				Codethink - Providing Genius