On Thu, May 07, 2020 at 04:06:31AM -0400, Mikulas Patocka wrote:
>
>
> On Wed, 6 May 2020, Mikulas Patocka wrote:
>
> >
> >
> > On Wed, 6 May 2020, Arnd Bergmann wrote:
> >
> > > On Wed, May 6, 2020 at 1:21 PM Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
> > >
> > > > /*
> > > > * The yet supported machines all access the RTC index register via
> > > > * an ISA port access but the way to access the date register differs ...
> > > > + *
> > > > + * The ISA bus on Alpha Avanti doesn't like back-to-back accesses,
> > > > + * we need to add a small delay.
> > > > */
> > > > #define CMOS_READ(addr) ({ \
> > > > outb_p((addr),RTC_PORT(0)); \
> > > > +udelay(2); \
> > > > inb_p(RTC_PORT(1)); \
> > >
> > >
> > > The inb_p() / outb_p() functions are meant to already have a delay in them,
> > > maybe we should just add it there for alpha?
> > >
> > > Arnd
> >
> > Yes, that is possible too - it fixes the real time clock hang for me.
> >
> >
> > -#define inb_p inb
> > -#define inw_p inw
> > -#define inl_p inl
> > +#define inb_p(x) (ndelay(300), inb(x))
> > +#define inw_p(x) (ndelay(300), inw(x))
> > +#define inl_p(x) (ndelay(300), inl(x))
> > #define outb_p outb
> > #define outw_p outw
> > #define outl_p outl
>
> 300ns was too low. We need at least 1400ns to fix the hang reliably.
>
> Mikulas
>
>
> From: Mikulas Patocka <mpatocka@xxxxxxxxxx>
>
> The patch 92d7223a74235054f2aa7227d207d9c57f84dca0 ("alpha: io: reorder
> barriers to guarantee writeX() and iowriteX() ordering #2") broke boot on
> the Alpha Avanti platform.
>
> The patch changes timing between accesses to the ISA bus, in particular,
> it reduces the time between "write" access and a subsequent "read" access.
>
> This causes lock-up when accessing the real time clock and serial ports.
>
> This patch fixes the real time clock by adding a small delay to the inb_p,
> inw_p and inl_p macros.
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Fixes: 92d7223a7423 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering #2")
> Cc: stable@xxxxxxxxxxxxxxx # v4.17+
>
> ---
> arch/alpha/include/asm/io.h | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
<snip>
This is not in a format that anyone can apply it in, please resend in a
proper way if you wish for it to be accepted.
thanks,
greg k-h
