linux-kernel - Re: [PATCH] m68k: mm: Remove check for VM

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Date:   Sat, 29 Jan 2022 10:55:30 +1100 (AEDT)
From:   Finn Thain <fthain@...ux-m68k.org>
To:     Michael Schmitz <schmitzmic@...il.com>
cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] m68k: mm: Remove check for VM_IO to fix deferred I/O

On Sat, 29 Jan 2022, Michael Schmitz wrote:

> Hi Geert,
> 
> for hwregs_present(), the exception fixup will handle any access error 
> (through send_fault_sig()), so this should continue to work.
> 
> Why the special handling of VM_IO pages? Maybe hp300 had marked all IO 
> register pages VM_IO to distinguish IO faults from VM faults...
> 
> The only other area I can imagine this might have an impact is the Mac's 
> pseudo-DMA - FInn might want to give this some testing.
> 

mac_scsi.c and mac_esp.c don't use ioremap(). They rely on head.S:

        mmu_map_eq      #0x50000000,#0x03000000,%d3

Having said that, I will run some tests if you still think it necessary.