linux-kernel - Re: [PATCH] pata_falcon: Add missing _

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Message-ID: <35a85d2f-ab6a-4ab7-85a8-626f1560a57d@linux-m68k.org>
Date:   Thu, 25 Nov 2021 12:06:27 +1100 (AEDT)
From:   Finn Thain <fthain@...ux-m68k.org>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
cc:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Michael Schmitz <schmitzmic@...il.com>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Jens Axboe <axboe@...nel.dk>, linux-ide@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pata_falcon: Add missing __iomem annotations

On Wed, 24 Nov 2021, Geert Uytterhoeven wrote:

> Thanks for your patch!
> 
> > --- a/drivers/ata/pata_falcon.c
> > +++ b/drivers/ata/pata_falcon.c
> > @@ -55,14 +55,14 @@ static unsigned int pata_falcon_data_xfer(struct ata_queued_cmd *qc,
> >         /* Transfer multiple of 2 bytes */
> >         if (rw == READ) {
> >                 if (swap)
> > -                       raw_insw_swapw((u16 *)data_addr, (u16 *)buf, words);
> > +                       raw_insw_swapw((u16 __iomem *)data_addr, (u16 *)buf, words);
> >                 else
> > -                       raw_insw((u16 *)data_addr, (u16 *)buf, words);
> > +                       raw_insw((u16 __iomem *)data_addr, (u16 *)buf, words);
> >         } else {
> >                 if (swap)
> > -                       raw_outsw_swapw((u16 *)data_addr, (u16 *)buf, words);
> > +                       raw_outsw_swapw((u16 __iomem *)data_addr, (u16 *)buf, words);
> >                 else
> > -                       raw_outsw((u16 *)data_addr, (u16 *)buf, words);
> > +                       raw_outsw((u16 __iomem *)data_addr, (u16 *)buf, words);
> 
> Can't you just drop the casts? data_addr is an __iomem void *.
> 

Yes, that works here (i.e. removing the data_addr casts and not the buf 
casts). But is it prudent?

Given the implementation of raw_in/out is subject to change, it seems like 
the original casts were defensive programming.

Here's an example of a recent regression that was fixed by casting a macro 
argument to a specific width:

https://lore.kernel.org/linuxppc-dev/79ae1f49-f6b1-e9ad-977d-0cc7e553c7b9@csgroup.eu/ 
https://lore.kernel.org/linuxppc-dev/08bbe7240b384016e0b2912ecf3bf5e2d25ef2c6.1636501628.git.fthain@linux-m68k.org/ 

BTW, that bug eventually got fixed using a different patch.

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/arch/powerpc/kernel/signal.h?id=5499802b2284331788a440585869590f1bd63f7f

Note that __get_user_sigset() still lacks width casts here, so it remains 
non-portable.