linux-kernel - Re: platform/x86: p2sb: Allow p2sb_bar() calls during PCI device probe

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Message-ID: <ZzxdXa-IsfHv2IFc@smile.fi.intel.com>
Date: Tue, 19 Nov 2024 11:41:49 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: "Daniel Walker (danielwa)" <danielwa@...co.com>
Cc: Hans de Goede <hdegoede@...hat.com>,
	Shinichiro Kawasaki <shinichiro.kawasaki@....com>,
	Ilpo J�rvinen <ilpo.jarvinen@...ux.intel.com>,
	Klara Modin <klarasmodin@...il.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Danil Rybakov <danilrybakov249@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xe-linux-external(mailer list)" <xe-linux-external@...co.com>
Subject: Re: platform/x86: p2sb: Allow p2sb_bar() calls during PCI device
 probe

On Mon, Nov 18, 2024 at 05:15:17PM +0000, Daniel Walker (danielwa) wrote:
> On Mon, Nov 18, 2024 at 05:00:52PM +0100, Hans de Goede wrote:
> > On 18-Nov-24 4:55 PM, Andy Shevchenko wrote:
> > > On Mon, Nov 18, 2024 at 02:35:44PM +0000, Daniel Walker (danielwa) wrote:
> > >> On Mon, Nov 18, 2024 at 03:49:32PM +0200, Andy Shevchenko wrote:
> > >>> On Mon, Nov 18, 2024 at 01:32:55PM +0000, Daniel Walker (danielwa) wrote:
> > >>>> On Mon, Nov 18, 2024 at 03:24:20PM +0200, Andy Shevchenko wrote:
> > >>>>> On Mon, Nov 18, 2024 at 12:40:16PM +0000, Daniel Walker (danielwa) wrote:

...

> > >>>>> Are you referring to LPC GPIO?
> > >>>>  
> > >>>>  I don't know the hardware well enough to say for certain. It's whatever device 8086:19dd is.
> > >>>
> > >>> This is device which represents p2sb. It's not a GPIO device you are talking
> > >>> about for sure. You can send privately more detailed info in case this is shouldn't
> > >>> be on public to me to understand what would be the best approach to fix your issue.
> > >>
> > >> Here's a comment,
> > >>
> > >> /* INTEL Denverton GPIO registers are accessible using SBREG_BAR(bar 0) as base */
> > >>
> > >> We have gpio wired to an FPGA and I believe the gpio line is used to reset the
> > >> fpga.
> > >>
> > >> So the pci resources attached to 8086:19dd can be used to access gpio of some
> > >> type. 
> > >>
> > >> I'm not a pci expert but on the 19bb device bar 0 we use the below offset to manipulate
> > >> the gpio,
> > >>
> > >> #define INTEL_GPIO_REG_RESET_OFFSET          0xC50578
> > >>
> > >> The comments suggest this is gpio 6. I would seems your reaction would be that
> > >> there is no gpio on the 19dd device. Maybe our driver is access gpio thru p2sb
> > >> or something like that.
> > >>
> > >> Does the offset above make sense to you in the context of the p2sb ?
> > > 
> > > Yes, everything makes sense. Please, enable lpc_ich driver and forget about
> > > talking to the p2sb memory mapped IO.
> > > 
> > > /* Offset data for Denverton GPIO controllers */
> > > static const resource_size_t dnv_gpio_offsets[DNV_GPIO_NR_RESOURCES] = {
> > > 	[DNV_GPIO_NORTH] = 0xc20000,
> > > 	[DNV_GPIO_SOUTH] = 0xc50000,
> > > };
> > > 
> > > So, you are using a pin from the Community "South" of the on-die Denverton GPIO.
> > > 
> > > In EDS this called GPIO_6, while in the driver it's pin 88, i.e. SMB3_IE0_DATA.
> > > 
> > > You will need to
> > > - enable lpc_ich driver (CONFIG_LPC_ICH)
> > > - enable Intel Denverton pin control driver (CONFIG_PINCTRL_DENVERTON)
> > > - replace your custom approach to:
> > >   - GPIO lookup table
> > >   - proper GPIO APIs, as gpiod_get() or alike
> > > 
> > > See how it was done in the current kernel code:
> > > 
> > > 8241b55f1ded ("drm/i915/dsi: Replace poking of VLV GPIOs behind the driver's back")
> > > a6c80bec3c93 ("leds: simatic-ipc-leds-gpio: Add GPIO version of Siemens driver")
> > > 
> > > Hans, there will be no need to fix anything if they implement correct access
> > > to the GPIO, i.e. via driver and board code with GPIO lookup tables.
> > 
> > Agreed, still I'm not sure how I feel about us hiding the previously unhidden P2SB.
> > 
> > OTOH I guess it may have only been unhidden in the BIOS to make the hack they
> > are using possible in the first place.
> 
> From a flexibility POV I would suggest if you can not hide it if it's not already
> hidden by the BIOS that would be better since some company may have a good
> reason to make a custom driver or to export the pci device to userspace thru
> UIO.

The previous emails used wrong terminology, the hidden device is left hidden, and
all the opposite: unhidden is not touched in this sense.

The problem there that for the initially unhidden devices we call pci_stop_...
which seems incorrect and needs to be fixed, indeed.

> The current situation is you can't make a custom driver if p2sb is enable
> with this additional patch even if you unhide the device inside the BIOS.

Yeah, but I do not consider that is anyhow related to upstream.

> In our case it seems like we could use the already existing solution with
> pinctrl, but others may not be able to do that or may not want to for different
> reasons.

Please, please, go with the pin control approach, let's not increase
the surface of the untested fields. Feel free to ask for a help from me
(and possibly Hans) if you need a such.

-- 
With Best Regards,
Andy Shevchenko