linux-kernel - Re: [PATCH -next 1/2] i2c: designware: Switch from using MMIO access to SMN access

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Message-ID: <YywwEvkZK1R9mJfE@smile.fi.intel.com>
Date:   Thu, 22 Sep 2022 12:51:14 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Borislav Petkov <bp@...e.de>, Hans de Goede <hdegoede@...hat.com>
Cc:     "Limonciello, Mario" <mario.limonciello@....com>,
        Jan Dąbroś <jsd@...ihalf.com>,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        jarkko.nikula@...ux.intel.com, wsa@...nel.org,
        rrangel@...omium.org, upstream@...ihalf.com,
        Muralidhara M K <muralimk@....com>,
        Naveen Krishna Chatradhi <nchatrad@....com>
Subject: Re: [PATCH -next 1/2] i2c: designware: Switch from using MMIO access
 to SMN access

+Cc: Hans (mentioned your name and was under impression that you are in Cc list already)

On Thu, Sep 22, 2022 at 12:49:15PM +0300, Andy Shevchenko wrote:
> On Wed, Sep 21, 2022 at 10:50:53PM +0200, Borislav Petkov wrote:
> > On Wed, Sep 21, 2022 at 03:19:26PM -0500, Limonciello, Mario wrote:
> > > Jan mentioned this in the commit message:
> > > 
> > > > The function which registers i2c-designware-platdrv is a
> > > > subsys_initcall that is executed before fs_initcall (when enumeration > of
> > > NB descriptors occurs).
> > > 
> > > So if it's not exported again, then it means that we somehow
> > > need to get i2c-designware-platdrv to register earlier too.
> > 
> > So I have this there:
> > 
> > /* This has to go after the PCI subsystem */
> > fs_initcall(init_amd_nbs);
> > 
> > as I need PCI. It itself does
> > 
> > arch_initcall(pci_arch_init);
> > 
> > so I guess init_amd_nbs() could be a subsys_initcall...
> > 
> > Or why is
> > 
> > subsys_initcall(dw_i2c_init_driver);
> > 
> > a subsys initcall in the first place?
> > 
> > Looking at
> > 
> >   104522806a7d ("i2c: designware: dw_i2c_init_driver as subsys initcall")
> > 
> > I don't see a particular reason why it should be a subsys_initcall...
> > 
> > In any case, this should be fixed without an export which was crap in
> > the first place.
> > 
> > Hm.
> 
> I'm speculating here, but IIRC the I2C controllers may serve PMICs on some
> platform that are required to be present earlier due to some ACPI code
> accessing them. This Hans de Goede can confirm or correct me.
> 
> Another case comes to my mind is that I2C framework wants to initialize I2C
> peripherals which were supplied via struct i2c_board_info on earlier stages.
> And again comes to the specifics of the certain peripherals that needs for
> power / reset / etc control, i.o.w. critical hardware for the platforms.
> 
> But it's still what I remember and I can be mistaken.

-- 
With Best Regards,
Andy Shevchenko