On Wed, Sep 30, 2015 at 4:17 PM, Duc Dang <dhdang@xxxxxxx> wrote:
> On Tue, Sep 29, 2015 at 9:47 AM, Rob Herring <robh@xxxxxxxxxx> wrote:
>> + several affected driver maintainers
>>
>> On Mon, Sep 28, 2015 at 6:05 PM, Russell King - ARM Linux
>> <linux@xxxxxxxxxxxxxxxx> wrote:
>>> On Mon, Sep 28, 2015 at 05:42:20PM -0500, Rob Herring wrote:
>>>> On Mon, Sep 28, 2015 at 5:08 PM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>>>> > Hi Rob,
>>>> >
>>>> > Russell pointed out a problem with 1f94a94f67e1 ("PCI: Add generic config
>>>> > accessors"). pci_generic_config_write32() does a read/modify/write if the
>>>> > size is less than 32 bits, so I think we have problem if this is used with
>>>> > 8- or 16-bit registers that contain RW1C bits. Any thoughts on how we can
>>>> > fix this?
>>>>
>>>> My series didn't change access sizes unless I made a made a mistake
>>>> somewhere, so the problem should have existed before.
>>>>
>>>> Is it known addresses we need to deal with? We could do special case
>>>> handling of certain addresses to mask out RW1C bits. This could be in
>>>> the generic functions or in wrappers around the generic functions.
>>>> There's already some similar examples of special address handling
>>>> IIRC.
>>>
>>> I think this originally came into being because Intel decided that their
>>> IOP platforms wouldn't support anything except 32-bit accesses, and
>>> cargo cult programming took over. I complained about it on the Intel IOP
>>> platforms, but obviously if the hardware doesn't support anything else
>>> then your stuck with it.
>>
>> What about SA1100 nanoengine?
>>
>> Others are Tegra, XGene, iproc, and maybe rcar. These are all
>> relatively active platforms, so hopefully some testing can be done.
>
> On X-Gene, so far I don't see anything strange after switching to use
> pci_generic_config_write32 with all the cards that I can test.
You mean switching to use pci_generic_config_write, right?
>
> But looks like it's still safer to use pci_generic_config_write
> instead as this will make sure no unexpected read-modify-write will
> happen?
Yes. You can also change xgene_pcie_config_read32 to use
pci_generic_config_read instead to simplify the function some.
Rob
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