linux-kernel - Re: [PATCH v4 07/14] PCI: cadence: Add new *ops* for CPU addr fixup

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Date:   Sat, 23 May 2020 06:54:18 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Rob Herring <robh@...nel.org>
CC:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Arnd Bergmann <arnd@...db.de>,
        Tom Joseph <tjoseph@...ence.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        PCI <linux-pci@...r.kernel.org>, <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-omap <linux-omap@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 07/14] PCI: cadence: Add new *ops* for CPU addr fixup

Hi Rob,

On 5/22/2020 10:15 PM, Rob Herring wrote:
> On Thu, May 21, 2020 at 5:35 AM Kishon Vijay Abraham I <kishon@...com> wrote:
>>
>> Hi Rob,
>>
>> On 5/21/2020 3:04 AM, Rob Herring wrote:
>>> On Wed, May 06, 2020 at 08:44:22PM +0530, Kishon Vijay Abraham I wrote:
>>>> Cadence driver uses "mem" memory resource to obtain the offset of
>>>> configuration space address region, memory space address region and
>>>> message space address region. The obtained offset is used to program
>>>> the Address Translation Unit (ATU). However certain platforms like TI's
>>>> J721E SoC require the absolute address to be programmed in the ATU and not
>>>> just the offset.
>>>
>>> Once again, Cadence host binding is broken (or at least the example is).
>>> The 'mem' region shouldn't even exist. It is overlapping the config
>>> space and 'ranges':
>>>
>>>             reg = <0x0 0xfb000000  0x0 0x01000000>,
>>>                   <0x0 0x41000000  0x0 0x00001000>,
>>>                   <0x0 0x40000000  0x0 0x04000000>;
>>>             reg-names = "reg", "cfg", "mem";
>>>
>>>             ranges = <0x02000000 0x0 0x42000000  0x0 0x42000000  0x0 0x1000000>,
>>>                      <0x01000000 0x0 0x43000000  0x0 0x43000000  0x0 0x0010000>;
>>>
>>>
>>> 16M of registers looks a bit odd. I guess it doesn't matter
>>> unless you have a 32-bit platform and care about your virtual
>>> space. Probably should have been 3 regions for LM, RP, and AT looking
>>> at the driver.
>>
>> The "mem" region in never ioremapped. However $patch removes requiring to add
>> "mem" memory resource.
> 
> I was referring to ioremapping 'reg' region.
> 
>>>
>>> Whatever outbound address translation you need should be based on
>>> 'ranges'.
>>
>> You mean we don't need to add "new *ops* for CPU addr fixup"?. The issue is
>> ranges provides CPU address and PCI address. The CPU will access whatever is
>> populated in ranges to access the PCI bus. However while programming the ATU,
>> we cannot use the CPU address provided in ranges directly (in some platforms)
>> because the controller does not see the full address and only the lower 28bits.
> 
> Okay, that is clearer as to what the difference is. I think this
> should be 2 patches. One dropping 'mem' usage and using a mask and the
> 2nd making the mask per platform.

hmm okay.
> 
> Really, the parent node of the PCI controller should probably have
> 'ranges' and you could extract a mask from that. Looks like that is
> what you had for DRA7... I'm not sure if ABI stability is important
> for the Cadence platform. I'd assume that's just some IP eval system
> and probably not?

Right TI's J721E should be the first HW platform to use Cadence in mainline.
> 
> Why do you need an ops here? All you need is a mask value.

So how do we get platform specific mask? Use a different binding to specify the
mask value?
> 
>> This similar restriction was there with Designware (mostly an integration
>> issue) and we used *ops* to fixup the address that has to be programmed in ATU.
>> The Designware initially used a wrapper so that ranges property can be directly
>> used [1]. However this approach was later removed in [2]
>>
>> [1] -> https://lore.kernel.org/patchwork/patch/468523/
>> [2] -> https://lkml.org/lkml/2015/10/16/232
> 
> So while you had the data for a mask in DT, the driver now hardcodes it?

Yes, that's correct. Which approach should we use for Cadence?

Thanks
Kishon