linux-kernel - Re: [PATCH 05/13] PCI: cadence: Add read and write accessors to perform only 32-bit accesses

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Date:   Thu, 19 Dec 2019 18:49:18 +0530
From:   Kishon Vijay Abraham I <kishon@...com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Andrew Murray <andrew.murray@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh+dt@...nel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-omap <linux-omap@...r.kernel.org>
Subject: Re: [PATCH 05/13] PCI: cadence: Add read and write accessors to
 perform only 32-bit accesses

Hi Arnd,

On 19/12/19 5:33 pm, Arnd Bergmann wrote:
> On Thu, Dec 19, 2019 at 12:54 PM Kishon Vijay Abraham I <kishon@...com> wrote:
>>
>> Hi Andrew,
>>
>> On 16/12/19 8:19 pm, Andrew Murray wrote:
>>> On Mon, Dec 09, 2019 at 02:51:39PM +0530, Kishon Vijay Abraham I wrote:
>>>> Certain platforms like TI's J721E allow only 32-bit register accesses.
>>>
>>> When I first read this I thought you meant only 32-bit accesses are allowed
>>> and not other sizes (such as 64-bit). However the limitation you address
>>> here is that the J721E allows only 32-bit *aligned* register accesses.
>>
>> It's both, it allows only 32-bit aligned accesses and the size should be
>> only 32 bits. That's why I always use "readl" in the APIs below.
> 
> In that case, can't you use the pci_generic_config_read32/write32
> functions with a cadence specific .map_bus() function?

pci_generic_config_read32() is for reading configuration space registers
only. The accessors I added here are for the controller IP configuration.

For the configuration space access I use
pci_generic_config_read32/write32()([PATCH 11/13] PCI: j721e: Add TI
J721E PCIe driver).

Thanks
Kishon