Re: [PATCH 1/2 v3] alpha: add a delay to inb_p, inb_w and inb_l

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

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@redhat.com> 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@redhat.com>
> 
> 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@redhat.com>
> Fixes: 92d7223a7423 ("alpha: io: reorder barriers to guarantee writeX() and iowriteX() ordering #2")
> Cc: stable@vger.kernel.org	# v4.17+
> 
> ---
>  arch/alpha/include/asm/io.h |    7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)

<snip>

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thanks,

greg k-h