linux-kernel - Re: [PATCH 1/4] platform/x86: simatic-ipc: add main driver for Siemens devices

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Date:   Fri, 5 Mar 2021 17:14:29 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Henning Schild <henning.schild@...mens.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux LED Subsystem <linux-leds@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        linux-watchdog@...r.kernel.org,
        Srikanth Krishnakar <skrishnakar@...il.com>,
        Jan Kiszka <jan.kiszka@...mens.com>,
        Gerd Haeussler <gerd.haeussler.ext@...mens.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Mark Gross <mgross@...ux.intel.com>,
        Pavel Machek <pavel@....cz>
Subject: Re: [PATCH 1/4] platform/x86: simatic-ipc: add main driver for
 Siemens devices

Hi,

On 3/5/21 4:42 PM, Andy Shevchenko wrote:
> On Thu, Mar 4, 2021 at 3:47 PM Hans de Goede <hdegoede@...hat.com> wrote:
>> On 3/4/21 11:11 AM, Andy Shevchenko wrote:
>>> On Thu, Mar 4, 2021 at 8:36 AM Henning Schild
>>> <henning.schild@...mens.com> wrote:
> 
> ...
> 
>>>> +u32 simatic_ipc_get_membase0(unsigned int p2sb)
>>>> +{
>>>> +       u32 bar0 = 0;
>>>
>>>> +#ifdef CONFIG_PCI
>>>
>>> It's ugly besides the fact that you have a dependency.
>>>
>>>> +       struct pci_bus *bus;
>>>
>>> Missed blank line.
>>>
>>>> +       /*
>>>> +        * The GPIO memory is bar0 of the hidden P2SB device. Unhide the device
>>>> +        * to have a quick look at it, before we hide it again.
>>>> +        * Also grab the pci rescan lock so that device does not get discovered
>>>> +        * and remapped while it is visible.
>>>> +        * This code is inspired by drivers/mfd/lpc_ich.c
>>>> +        */
>>>> +       bus = pci_find_bus(0, 0);
>>>> +       pci_lock_rescan_remove();
>>>> +       pci_bus_write_config_byte(bus, p2sb, 0xE1, 0x0);
>>>> +       pci_bus_read_config_dword(bus, p2sb, PCI_BASE_ADDRESS_0, &bar0);
>>>> +
>>>> +       bar0 &= ~0xf;
>>>> +       pci_bus_write_config_byte(bus, p2sb, 0xE1, 0x1);
>>>> +       pci_unlock_rescan_remove();
>>>> +#endif /* CONFIG_PCI */
>>>> +       return bar0;
>>>> +}
>>>> +EXPORT_SYMBOL(simatic_ipc_get_membase0);
>>>
>>> Oy vey! I know what this is and let's do it differently. I have some
>>> (relatively old) patch series I can send you privately for testing.
>>
>> This bit stood out the most to me too, it would be good if we can this fixed
>> in some cleaner work. So I'm curious how things will look with Andy's work
>> integrated.
>>
>> Also I don't think this should be exported. Instead this (or its replacement)
>> should be used to get the address for an IOMEM resource to add the platform
>> devices when they are instantiated. Then the platform-dev drivers can just
>> use the regular functions to get their resources instead of relying on this
>> module.
> 
> I have published a WIP branch [1]. I have no means to test (I don't
> know what hardware at hand I can use right now), but I made it compile
> after 4 years of gathering dust...

So I took a quick look at the following 2 commits:

"platform/x86: p2sb: New Primary to Sideband bridge support library"
"mfd: lpc_ich: Switch to generic p2sb_bar()"

And this looks good to me, although compared to the code from this
patch-set you are missing the pci_lock_rescan_remove(); and
pci_unlock_rescan_remove(); calls.

> Feel free to give any kind of comments or share your ideas on how it
> can be improved (the above idea on IOMEM resource is interesting, but
> devices are PCI, not sure how this can be done).

The code added by this patch introduces a register_platform_devices()
function which creates a bunch of platform-devices; and then the
device-drivers for those call simatic_ipc_get_membase0() to get their
base-address.

My suggestion was to instead put the  simatic_ipc_get_membase0() call
inside the code instantiating the platform devices and to add the
base-address for that pdev as IOMEM resource to the instantiated
platform-devices.

I hope this helps to clarify what I was trying to say.

Regards,

Hans