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From:   Geert Uytterhoeven <geert@linux-m68k.org>
Date:   Fri, 4 Dec 2020 09:38:25 +0100
Message-ID: <CAMuHMdUYwUPWzhBD+MWJsjBvmb31T0=2j8d0_-f9Q0ocfBAs9A@mail.gmail.com>
Subject: Re: [PATCH] scsi/NCR5380: Remove in_interrupt() test
To:     Finn Thain <fthain@telegraphics.com.au>
Cc:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Michael Schmitz <schmitzmic@gmail.com>,
        "James E.J. Bottomley" <jejb@linux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@oracle.com>,
        "Ahmed S. Darwish" <a.darwish@linutronix.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        scsi <linux-scsi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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Hi Finn,

On Fri, Dec 4, 2020 at 12:11 AM Finn Thain <fthain@telegraphics.com.au> wrote:
> > --- a/drivers/scsi/g_NCR5380.c
> > +++ b/drivers/scsi/g_NCR5380.c
> > @@ -529,14 +529,14 @@ static inline int generic_NCR5380_precv(struct NCR5380_hostdata *hostdata,
> >               if (start == len - 128) {
> >                       /* Ignore End of DMA interrupt for the final buffer */
> >                       if (NCR5380_poll_politely(hostdata, hostdata->c400_ctl_status,
> > -                                               CSR_HOST_BUF_NOT_RDY, 0, HZ / 64) < 0)
> > +                                               CSR_HOST_BUF_NOT_RDY, 0, 0) < 0)
>
> You've put your finger on a known problem with certain
> NCR5380_poll_politely() call sites. That is, the nominal timeout, HZ / 64,
> is meaningless because it is ignored in atomic context. So you may as well
> specify 0 jiffies at these call sites. (There will be a 1 jiffy timeout
> applied regardless.)

Notwithstanding HZ / 64 breaks if HZ < 64.

Possible values of HZ in the kernel:

24
32
48
64
100
128
200
250
256
300
500
1000
1024
1200

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds