RE: [PATCH 1/3] ARM: at91: flush the L2 cache before entering cpu idle

[<Wenyou.Yang@microchip.com>]

Hi Jean-Jacques,

> -----Original Message-----
> From: Jean-Jacques Hiblot [mailto:jjhiblot@gmail.com]
> Sent: 2017年1月11日 0:51
> To: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> Cc: Wenyou Yang - A41535 <Wenyou.Yang@microchip.com>; Mark Rutland
> <mark.rutland@arm.com>; devicetree <devicetree@vger.kernel.org>; Russell
> King <linux@arm.linux.org.uk>; Wenyou Yang - A41535
> <Wenyou.Yang@microchip.com>; Nicolas Ferre <nicolas.ferre@atmel.com>;
> Linux Kernel Mailing List <linux-kernel@vger.kernel.org>; Rob Herring
> <robh+dt@kernel.org>; linux-arm-kernel@lists.infradead.org
> Subject: Re: [PATCH 1/3] ARM: at91: flush the L2 cache before entering cpu idle
> 
> 2017-01-10 17:18 GMT+01:00 Alexandre Belloni
> <alexandre.belloni@free-electrons.com>:
> > I though a bit more about it, and I don't really like the new
> > compatible string. I don't feel this should be necessary.
> >
> > What about the following:
> >
> > diff --git a/arch/arm/mach-at91/pm.c b/arch/arm/mach-at91/pm.c index
> > b4332b727e9c..0333aca63e44 100644
> > --- a/arch/arm/mach-at91/pm.c
> > +++ b/arch/arm/mach-at91/pm.c
> > @@ -53,6 +53,7 @@ extern void at91_pinctrl_gpio_resume(void);  static
> > struct {
> >         unsigned long uhp_udp_mask;
> >         int memctrl;
> > +       bool has_l2_cache;
> >  } at91_pm_data;
> >
> >  void __iomem *at91_ramc_base[2];
> > @@ -267,6 +268,11 @@ static void at91_ddr_standby(void)
> >         u32 lpr0, lpr1 = 0;
> >         u32 saved_lpr0, saved_lpr1 = 0;
> >
> 
> > +       if (at91_pm_data.has_l2_cache) {
> > +               flush_cache_all();
> what is the point of calling flush_cache_all() here ? Do we really care that dirty
> data in L1 is written to DDR ? I may be missing something but to me it's just extra
> latency.

Are you mean use outer_flush_all() to flush all cache lines in the outer cache only?

> > +               outer_disable();
> It seems to me that if there's no L2 cache, then outer_disable()  is a no-op. It
> could be called unconditionally.
> > +       }
> > +
> >         if (at91_ramc_base[1]) {
> >                 saved_lpr1 = at91_ramc_read(1, AT91_DDRSDRC_LPR);
> >                 lpr1 = saved_lpr1 & ~AT91_DDRSDRC_LPCB; @@ -287,6
> > +293,9 @@ static void at91_ddr_standby(void)
> >         at91_ramc_write(0, AT91_DDRSDRC_LPR, saved_lpr0);
> >         if (at91_ramc_base[1])
> >                 at91_ramc_write(1, AT91_DDRSDRC_LPR, saved_lpr1);
> > +
> > +       if (at91_pm_data.has_l2_cache)
> > +               outer_resume();
> 
> same remark as for outer_disable()
> 
> Jean-Jacques
> 
> >  }
> >
> >  /* We manage both DDRAM/SDRAM controllers, we need more than one
> > value
> >  * to
> > @@ -353,6 +362,11 @@ static __init void at91_dt_ramc(void)
> >                 return;
> >         }
> >
> > +       np = of_find_compatible_node(NULL, NULL, "arm,pl310-cache");
> > +       if (np)
> > +               at91_pm_data.has_l2_cache = true;
> > +       of_node_put(np);
> > +
> >         at91_pm_set_standby(standby);
> >  }
> >
> >
> > This has the following benefits:
> >  - everybody will have the fix, regardless of whether the dtb is
> > updated
> >  - has_l2_cache can be used later in at91_pm_suspend instead of calling
> >    it unconditionnaly (I'll send a patch)
> >
> >
> > On 06/01/2017 at 14:59:45 +0800, Wenyou Yang wrote :
> >> For the SoCs such as SAMA5D2 and SAMA5D4 which have L2 cache, flush
> >> the L2 cache first before entering the cpu idle.
> >>
> >> Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
> >> ---
> >>
> >>  arch/arm/mach-at91/pm.c       | 19 +++++++++++++++++++
> >>  drivers/memory/atmel-sdramc.c |  1 +
> >>  2 files changed, 20 insertions(+)
> >>
> >> diff --git a/arch/arm/mach-at91/pm.c b/arch/arm/mach-at91/pm.c index
> >> b4332b727e9c..1a60dede1a01 100644
> >> --- a/arch/arm/mach-at91/pm.c
> >> +++ b/arch/arm/mach-at91/pm.c
> >> @@ -289,6 +289,24 @@ static void at91_ddr_standby(void)
> >>               at91_ramc_write(1, AT91_DDRSDRC_LPR, saved_lpr1);  }
> >>
> >> +static void at91_ddr_cache_standby(void) {
> >> +     u32 saved_lpr;
> >> +
> >> +     flush_cache_all();
> >> +     outer_disable();
> >> +
> >> +     saved_lpr = at91_ramc_read(0, AT91_DDRSDRC_LPR);
> >> +     at91_ramc_write(0, AT91_DDRSDRC_LPR, (saved_lpr &
> >> +                     (~AT91_DDRSDRC_LPCB)) |
> >> + AT91_DDRSDRC_LPCB_SELF_REFRESH);
> >> +
> >> +     cpu_do_idle();
> >> +
> >> +     at91_ramc_write(0, AT91_DDRSDRC_LPR, saved_lpr);
> >> +
> >> +     outer_resume();
> >> +}
> >> +
> >>  /* We manage both DDRAM/SDRAM controllers, we need more than one
> value to
> >>   * remember.
> >>   */
> >> @@ -324,6 +342,7 @@ static const struct of_device_id const ramc_ids[]
> __initconst = {
> >>       { .compatible = "atmel,at91sam9260-sdramc", .data =
> at91sam9_sdram_standby },
> >>       { .compatible = "atmel,at91sam9g45-ddramc", .data = at91_ddr_standby },
> >>       { .compatible = "atmel,sama5d3-ddramc", .data =
> >> at91_ddr_standby },
> >> +     { .compatible = "atmel,sama5d4-ddramc", .data =
> >> + at91_ddr_cache_standby },
> >>       { /*sentinel*/ }
> >>  };
> >>
> >> diff --git a/drivers/memory/atmel-sdramc.c
> >> b/drivers/memory/atmel-sdramc.c index b418b39af180..7e5c5c6c1348
> >> 100644
> >> --- a/drivers/memory/atmel-sdramc.c
> >> +++ b/drivers/memory/atmel-sdramc.c
> >> @@ -48,6 +48,7 @@ static const struct of_device_id atmel_ramc_of_match[]
> = {
> >>       { .compatible = "atmel,at91sam9260-sdramc", .data =
> &at91rm9200_caps, },
> >>       { .compatible = "atmel,at91sam9g45-ddramc", .data =
> &at91sam9g45_caps, },
> >>       { .compatible = "atmel,sama5d3-ddramc", .data = &sama5d3_caps,
> >> },
> >> +     { .compatible = "atmel,sama5d4-ddramc", .data = &sama5d3_caps,
> >> + },
> >>       {},
> >>  };
> >>
> >> --
> >> 2.11.0
> >>
> >
> > --
> > Alexandre Belloni, Free Electrons
> > Embedded Linux and Kernel engineering
> > http://free-electrons.com
> >
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