Re: [PATCH] iomap: Fix -Wmissing-prototypes on UM

[Andy Shevchenko]

On Mon, Feb 03, 2025 at 02:34:11PM +0100, Arnd Bergmann wrote:
> On Mon, Feb 3, 2025, at 14:23, Andy Shevchenko wrote:
> > On Mon, Feb 03, 2025 at 02:08:35PM +0100, Arnd Bergmann wrote:
> >
> >> > I like the lib/* and include/* cleanup but PTP probably should stay as is.
> >> > OTOH WWAN case most likely had been tested on 64-bit platforms only and
> >> > proves that readq()/writeq() works there, so it's okay to unify.
> >> 
> >> Ok, I'll try to split it up into sensible patches then. For ptp
> >> (both ixp46x and pch), these are the options I see:
> 
> Update: While splitting out the wwan patch, I see that this would
> revert 7d5a7dd5a358 ("net: wwan: t7xx: Split 64bit accesses to fix
> alignment issues"), so that driver also needs to keep using the
> split accessors, at least for some of the registers. From what
> I can tell, the problem here is that REG_CLDMA_UL_START_ADDRL_0
> is not a multiple of 8, and arm64 CPUs require MMIO registers
> to be naturally aligned.
> 
> If that is the cause of the problem, this means that on x86-64
> the unaligned readq() is still used but happens to work.
> Once I change linux/io-64-nonatomic-lo-hi.h, it will split
> the access on x86-64 and other using GENERIC_IOMAP as well.
> 
> The accesses to ATR_PCIE_WIN0_T0_TRSL_ADDR and
> ATR_PCIE_WIN0_T0_ATR_PARAM_SRC_ADDR can probably use ioread64()
> because they are on aligned addresses, but it should be safe
> to just leave this driver alone and keep all the split
> accesses.

Interesting. I haven't followed the development of that driver, so it seems it
gets some fixes over the time. In previous reply I was under impression that
the code in question was initially written by Intel and hence was assumed to
split (because readq()/writeq() usually works there and no explicit treatment
is needed in the most of the cases).

-- 
With Best Regards,
Andy Shevchenko