linux-kernel - Re: [PATCH] i2c: piix4: Replace piix4_smbus driver's cd6h/cd7h port io accesses with mmio accesses

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Date:   Tue, 18 Jan 2022 14:09:56 +0100
From:   Jean Delvare <jdelvare@...e.de>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Wolfram Sang <wsa@...nel.org>, Terry Bowman <Terry.Bowman@....com>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        linux-watchdog@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Robert Richter <rrichter@....com>
Subject: Re: [PATCH] i2c: piix4: Replace piix4_smbus driver's cd6h/cd7h port
 io accesses with mmio accesses

On Thu, 13 Jan 2022 12:24:41 +0200, Andy Shevchenko wrote:
> On Thu, Jan 13, 2022 at 9:42 AM Wolfram Sang <wsa@...nel.org> wrote:
> > > > On top of that I'm wondering why slow I/O is used? Do we have anything
> > > > that really needs that or is it simply a cargo-cult?  
> > >
> > > The efch SMBUS & WDT previously only supported a port I/O interface
> > > (until recently) and thus dictated the HW access method.  
> >
> > Is this enough information to start v2 of this series? Or does the
> > approach need more discussion?  
> 
> I dunno why slow I/O is chosen, but it only affects design (read:
> ugliness) of the new code.

I've been wondering about the use of slow (*_p) I/O accessors for some
time too. All the SMBus controller drivers doing that originate from the
lm_sensors project (i2c-ali1535, i2c-ali1563, i2c-ali15x3, i2c-amd756,
i2c-i801, i2c-nforce2, i2c-piix4 and i2c-viapro). So basically *all*
SMBus controller drivers for non-embedded x86.

I suspect that most of this is the result of copy-and-paste from one
driver to the next as support for different chipsets was added in the
late 90's and early 2000's. I wouldn't be surprised if most, if not
all, can be replaced with non-pausing counterparts. But I've been too
shy to give it a try so far.

I must say I find it pretty funny that Andy is asking about it in the
i2c-piix4 driver when the i2c-i801 driver, which he's been helping with
quite a lot in the last few years, does exactly the same.

-- 
Jean Delvare
SUSE L3 Support