Re: [JUST RFC] ARM: DIGIC: add csrc-dummy

[Antony Pavlov <antonynpavlov@gmail.com>]

On Sun, 15 Dec 2013 20:30:16 +0100
Alexander Aring <alex.aring@gmail.com> wrote:

> Hi Antony,
> 
> On Sun, Dec 15, 2013 at 07:02:05PM +0400, Antony Pavlov wrote:
> > The clocksource csrc-timer driver that uses DIGIC
> > hardware TIMER2 perfectrly works on Canon A1100,
> > but does not works on Canon EOS 600D.
> > IMHO we need additional timer initialisation.
> > 
> > This patch introduces a quick-and-dirty termporary
> > solution for this situation: a clocksource driver that
> > does not use any hardware at all.
> > 
> > Also this driver is very handy for running barebox
> > on Magic Lantern EOS qemu-based emulator as
> > the emulator does not realize timer counter register at all!
> > 
> > Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>
> > ---
> >  arch/arm/mach-digic/Kconfig      |  3 +++
> >  arch/arm/mach-digic/Makefile     |  1 +
> >  arch/arm/mach-digic/csrc-dummy.c | 49 ++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 53 insertions(+)
> >  create mode 100644 arch/arm/mach-digic/csrc-dummy.c
> > 
> > diff --git a/arch/arm/mach-digic/Kconfig b/arch/arm/mach-digic/Kconfig
> > index 557cad4..d0524bc 100644
> > --- a/arch/arm/mach-digic/Kconfig
> > +++ b/arch/arm/mach-digic/Kconfig
> > @@ -16,4 +16,7 @@ config ARCH_TEXT_BASE
> >  config DIGIC_CSRC_TIMER
> >  	bool
> >  
> > +config DIGIC_CSRC_DUMMY
> > +	bool
> > +
> >  endif
> > diff --git a/arch/arm/mach-digic/Makefile b/arch/arm/mach-digic/Makefile
> > index 1d7cb72..31e5ac1 100644
> > --- a/arch/arm/mach-digic/Makefile
> > +++ b/arch/arm/mach-digic/Makefile
> > @@ -1,2 +1,3 @@
> >  obj-y += core.o
> >  obj-$(CONFIG_DIGIC_CSRC_TIMER) += csrc-timer.o
> > +obj-$(CONFIG_DIGIC_CSRC_DUMMY) += csrc-dummy.o
> > diff --git a/arch/arm/mach-digic/csrc-dummy.c b/arch/arm/mach-digic/csrc-dummy.c
> > new file mode 100644
> > index 0000000..68c68a3
> > --- /dev/null
> > +++ b/arch/arm/mach-digic/csrc-dummy.c
> > @@ -0,0 +1,49 @@
> > +/*
> > + * Copyright (C) 2013 Antony Pavlov <antonynpavlov@gmail.com>
> > + *
> > + * This file is part of barebox.
> > + * See file CREDITS for list of people who contributed to this project.
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2
> > + * as published by the Free Software Foundation.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + *
> > + */
> > +
> > +#include <init.h>
> > +#include <clock.h>
> > +
> > +#include <stdio.h>
> > +
> > +static uint64_t dummy_counter;
> > +
> > +static uint64_t dummy_cs_read(void)
> > +{
> > +	dummy_counter += 2000;
> > +	return dummy_counter;
> > +}
> > +
> So if I understand it right, you assume here that the instructions to
> read this value will take 0.02 ms?

It is not quite. I don't assume initially the time to read this value.
This value ("2000") was a suboptimal value for __specific board__
under the __specific circumstances__.
I have selected this value after several experiments.

-- 
Best regards,
  Antony Pavlov

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