Re: [PATCH 1/5] soc: mediatek: Add infracfg misc driver support

[Sascha Hauer <s.hauer-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>]

Hi Daniel,

On Fri, May 15, 2015 at 10:17:33PM +0800, Daniel Kurtz wrote:
> Hi Sascha,
> 
> On Tue, May 12, 2015 at 3:23 AM, Sascha Hauer <s.hauer-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org> wrote:
> > This adds support for some miscellaneous bits of the infracfg controller.
> > The mtk_infracfg_set/clear_bus_protection functions are necessary for
> > the scpsys power domain driver to handle the bus protection bits which
> > are contained in the infacfg register space.
> >
> > Signed-off-by: Sascha Hauer <s.hauer-bIcnvbaLZ9MEGnE8C9+IrQ@public.gmane.org>
> > ---
> >  drivers/soc/mediatek/Kconfig        |  9 +++++
> >  drivers/soc/mediatek/Makefile       |  1 +
> >  drivers/soc/mediatek/mtk-infracfg.c | 80 +++++++++++++++++++++++++++++++++++++
> >  3 files changed, 90 insertions(+)
> >  create mode 100644 drivers/soc/mediatek/mtk-infracfg.c
> >
> > diff --git a/drivers/soc/mediatek/Kconfig b/drivers/soc/mediatek/Kconfig
> > index bcdb22d..6fae66f 100644
> > --- a/drivers/soc/mediatek/Kconfig
> > +++ b/drivers/soc/mediatek/Kconfig
> > @@ -9,3 +9,12 @@ config MTK_PMIC_WRAP
> >           Say yes here to add support for MediaTek PMIC Wrapper found
> >           on different MediaTek SoCs. The PMIC wrapper is a proprietary
> >           hardware to connect the PMIC.
> > +
> > +config MTK_INFRACFG
> 
> nit: Could you alphabetize these config options - so this one before
> MTK_PMIC_WRAP
> 
> > +       tristate "MediaTek INFRACFG Support"
> > +       depends on ARCH_MEDIATEK
> 
> I've seen several drivers like this now:
> 
>   depends on ARCH_MEDIATEK || COMPILE_TEST
> 
> 
> > +       select REGMAP
> > +       help
> > +         Say yes here to add support for the MediaTek INFRACFG controller. The
> > +         INFRACFG controller contains various infrastructure registers not
> > +         directly associated to any device.
> > diff --git a/drivers/soc/mediatek/Makefile b/drivers/soc/mediatek/Makefile
> > index ecaf4de..ce39119 100644
> > --- a/drivers/soc/mediatek/Makefile
> > +++ b/drivers/soc/mediatek/Makefile
> > @@ -1 +1,2 @@
> >  obj-$(CONFIG_MTK_PMIC_WRAP) += mtk-pmic-wrap.o
> > +obj-$(CONFIG_MTK_INFRACFG) += mtk-infracfg.o
> 
> alphabetize here, too.
> 
> > diff --git a/drivers/soc/mediatek/mtk-infracfg.c b/drivers/soc/mediatek/mtk-infracfg.c
> > new file mode 100644
> > index 0000000..b3ebfae
> > --- /dev/null
> > +++ b/drivers/soc/mediatek/mtk-infracfg.c
> > @@ -0,0 +1,80 @@
> > +#include <linux/regmap.h>
> > +#include <linux/export.h>
> > +#include <linux/jiffies.h>
> > +#include <linux/soc/mediatek/infracfg.h>
> > +#include <asm/processor.h>
> 
> and... alphabetize headers here.
> 
> I'm not sure if people care, but I find it makes it much easier to
> merge/add things later if these lists are already sorted.
> Same "please alphabetize" comments for the mtk-scpsys patch, so I
> won't repeat them.
> 
> > +
> > +#define INFRA_TOPAXI_PROTECTEN         0x0220
> > +#define INFRA_TOPAXI_PROTECTSTA1       0x0228
> > +
> > +/**
> > + * mtk_infracfg_set_bus_protection - enable bus protection
> > + * @regmap: The infracfg regmap
> > + * @mask: The mask containing the protection bits to be enabled.
> > + *
> > + * This function enables the bus protection bits for disabled power
> > + * domains so that the system does not hanf when some unit accesses the
> > + * bus while in power down.
> > + */
> > +int mtk_infracfg_set_bus_protection(struct regmap *infracfg, u32 mask)
> > +{
> > +       unsigned long expired;
> > +       u32 val;
> > +       int ret;
> > +
> > +       regmap_update_bits(infracfg, INFRA_TOPAXI_PROTECTEN, mask, mask);
> > +
> > +       expired = jiffies + HZ;
> > +
> > +       while (1) {
> > +               ret = regmap_read(infracfg, INFRA_TOPAXI_PROTECTSTA1, &val);
> > +               if (ret)
> > +                       return ret;
> > +
> > +               if ((val & mask) == mask)
> > +                       break;
> > +
> > +               cpu_relax();
> > +               if (time_after(jiffies, expired))
> > +                       return -EIO;
> 
> I think we should check for timeout first, and then cpu_relax() if
> there is still time left (here and in
> mtk_infracfg_clear_bus_protection()).  Otherwise we end up doing one
> final cpu_relax() without rechecking the register we are polling
> (again, I have the same comment for the timeout loops in mtk-scpsys).

I think cpu_relax() delays execution in the order of microseconds (I
don't actually know, just a guess), so if the timeout is a second the
order doesn't really matter. What can happen though is an interrupt
after the (val & mask) test but before the timeout check. So to be
truly correct we have to repeat the (val & mask) test after the
time_after() check. Is that what you want?

> 
> Also, shouldn't we return -ETIMEOUT if we timeout?

I dunno. Probably the operation operation timed out because of an IO
error. I'll change it to -ETIMEDOUT.

Sascha

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