Re: [PATCH v5 03/14] PCI: cadence: Convert all r/w accessors to perform only 32-bit accesses

[Kishon Vijay Abraham I]

Hi Rob,

On 5/22/2020 9:24 PM, Rob Herring wrote:
> On Thu, May 21, 2020 at 9:37 PM Kishon Vijay Abraham I <kishon@xxxxxx> wrote:
>>
>> Certain platforms like TI's J721E using Cadence PCIe IP can perform only
>> 32-bit accesses for reading or writing to Cadence registers. Convert all
>> read and write accesses to 32-bit in Cadence PCIe driver in preparation
>> for adding PCIe support in TI's J721E SoC.
> 
> Looking more closely I don't think cdns_pcie_ep_assert_intx is okay
> with this and never can be given the PCI_COMMAND and PCI_STATUS
> registers are in the same word (IIRC, that's the main reason 32-bit
> config space accesses are broken). So this isn't going to work at

right, PCI_STATUS has write '1' to clear bits and there's a chance that it
could be reset while raising legacy interrupt. While this cannot be avoided for
TI's J721E, other platforms doesn't have to have this limitation.
> least for EP accesses. And maybe you need a custom .raise_irq() hook
> to minimize any problems (such as making the RMW atomic at least from
> the endpoint's perspective).

This is to make sure EP doesn't update in-consistent state when RC is updating
the PCI_STATUS register? Since this involves two different systems, how do we
make this atomic?

Thanks
Kishon