linux-kernel - Re: [PATCH 2/2] ARM: OMAP4: Store reboot mode to SAR scratchpad memory before restart

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Message-ID: <1459627588.12073.30.camel@paulk.fr>
Date:	Sat, 02 Apr 2016 22:06:28 +0200
From:	Paul Kocialkowski <contact@...lk.fr>
To:	Nishanth Menon <nm@...com>, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org, "Mahaveer, Vishal" <vishalm@...com>
Cc:	Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH 2/2] ARM: OMAP4: Store reboot mode to SAR scratchpad
 memory before restart

Hi,

Le mardi 29 mars 2016 à 18:50 -0500, Nishanth Menon a écrit :
> On 03/29/2016 02:25 PM, Paul Kocialkowski wrote:
> > 
> > This adds support for storing the reboot mode command to SAR scratchpad
> > memory,
> > at a location compatible with TI kernels, so that bootloaders can grab the
> > reboot mode and act upon it.
> > 
> > Currently, upstream U-Boot has support for this feature on OMAP4.
> Since this impacts more SoCs than OMAP4, + Vishal.
> 
> > 
> > 
> > Signed-off-by: Paul Kocialkowski <contact@...lk.fr>
> > ---
> >  arch/arm/mach-omap2/common.h           |  1 +
> >  arch/arm/mach-omap2/omap4-common.c     | 12 ++++++++++++
> >  arch/arm/mach-omap2/omap4-restart.c    |  2 +-
> >  arch/arm/mach-omap2/omap4-sar-layout.h |  3 +++
> >  4 files changed, 17 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/arm/mach-omap2/common.h b/arch/arm/mach-omap2/common.h
> > index f7666b9..d773385 100644
> > --- a/arch/arm/mach-omap2/common.h
> > +++ b/arch/arm/mach-omap2/common.h
> > @@ -258,6 +258,7 @@ extern bool gic_dist_disabled(void);
> >  extern void gic_timer_retrigger(void);
> >  extern void omap_smc1(u32 fn, u32 arg);
> >  extern void __iomem *omap4_get_sar_ram_base(void);
> > +extern void omap4_sar_ram_write_boot_mode(const char *cmd);
> >  extern void omap_do_wfi(void);
> >  
> >  #ifdef CONFIG_SMP
> > diff --git a/arch/arm/mach-omap2/omap4-common.c b/arch/arm/mach-omap2/omap4-
> > common.c
> > index 949696b..85f251e 100644
> > --- a/arch/arm/mach-omap2/omap4-common.c
> > +++ b/arch/arm/mach-omap2/omap4-common.c
> > @@ -265,6 +265,18 @@ void __iomem *omap4_get_sar_ram_base(void)
> >  	return sar_ram_base;
> >  }
> >  
> > +void omap4_sar_ram_write_boot_mode(const char *cmd)
> > +{
> > +	void __iomem *sar_base;
> > +
> > +	sar_base = omap4_get_sar_ram_base();
> > +
> > +	if (!cmd)
> > +		strncpy(sar_base + BOOT_MODE_OFFSET, "", BOOT_MODE_SIZE);
> > +	else
> > +		strncpy(sar_base + BOOT_MODE_OFFSET, cmd, BOOT_MODE_SIZE);
> > +}
> > 
> > +
> >  /*
> >   * SAR RAM used to save and restore the HW
> >   * context in low power modes
> > diff --git a/arch/arm/mach-omap2/omap4-restart.c b/arch/arm/mach-
> > omap2/omap4-restart.c
> > index e17136a..74f29b5 100644
> > --- a/arch/arm/mach-omap2/omap4-restart.c
> > +++ b/arch/arm/mach-omap2/omap4-restart.c
> > @@ -22,6 +22,6 @@
> >   */
> >  void omap44xx_restart(enum reboot_mode mode, const char *cmd)
> >  {
> > -	/* XXX Should save 'cmd' into scratchpad for use after reboot */
> > +	omap4_sar_ram_write_boot_mode(cmd);
> I think you might have noticed that the function gets reused for more
> SoCs than just OMAP4. Did you consider the impact on other SoCs?

I did not. In fact, I only figured that newer platforms are also using that code
after writing that patch up. The name is quite confusing IMO, but then the whole
mach directory is named "omap2", so I get the logic here.

I have an OMAP5 uEVM board at disposal to test, so I'll at least check it at
runtime on it.

> A) I would suggest you should download the TRMs from TI website and
> check the impact this change has for all other platforms.

Do you think it's enough to check for the SAR scratchpad presence at the same
address, or is there something more I should look into?

> B) on certain platforms like DRA74 SoCs, warm reset cannot be used -
> instead all warm resets are converted to cold resets. what that means is
> that you'd probably want to update the reset reason to a PMIC scratch
> pad register.

I understand, but since I have no means of testing this, I'm not very
comfortable writing up an implementation. Either way, if SAR memory is there on
DRA74, this won't cause any trouble. And I'd be more comfortable with someone
else adding DRA74 support later.

What do you think?

> >  	omap_prm_reset_system();
> >  }
> > diff --git a/arch/arm/mach-omap2/omap4-sar-layout.h b/arch/arm/mach-
> > omap2/omap4-sar-layout.h
> > index 792b106..247b2bf 100644
> > --- a/arch/arm/mach-omap2/omap4-sar-layout.h
> > +++ b/arch/arm/mach-omap2/omap4-sar-layout.h
> > @@ -20,6 +20,7 @@
> >  #define SAR_BANK4_OFFSET		0x3000
> >  
> >  /* Scratch pad memory offsets from SAR_BANK1 */
> > +#define BOOT_MODE_OFFSET			0xa0c
> >  #define SCU_OFFSET0				0xfe4
> >  #define SCU_OFFSET1				0xfe8
> >  #define OMAP_TYPE_OFFSET			0xfec
> > @@ -28,6 +29,8 @@
> >  #define L2X0_AUXCTRL_OFFSET			0xff8
> >  #define L2X0_PREFETCH_CTRL_OFFSET		0xffc
> >  
> > +#define BOOT_MODE_SIZE				0xf
> > +
> >  /* CPUx Wakeup Non-Secure Physical Address offsets in SAR_BANK3 */
> >  #define CPU0_WAKEUP_NS_PA_ADDR_OFFSET		0xa04
> >  #define CPU1_WAKEUP_NS_PA_ADDR_OFFSET		0xa08
> > 
> 
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