linux-kernel - Re: [PATCH] power: reset: at91-reset: enable I-cache for at91sam9260

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Date:   Tue, 16 Oct 2018 13:30:24 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <jonas@...ital-systems.com>, <linux-kernel@...r.kernel.org>
CC:     <sre@...nel.org>, <Nicolas.Ferre@...rochip.com>,
        <alexandre.belloni@...tlin.com>, <linux-pm@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] power: reset: at91-reset: enable I-cache for
 at91sam9260_reset

Hi Jonas,

On 07.10.2018 15:57, Jonas Danielsson wrote:
> From: Jonas Danielsson <jonas@...ital-systems.com>
> 
> This fixes a bug where our embedded system (AT91SAM9260 based) would
> hang at reboot. At the most we managed 16 boot loops without a hang.
> 
> With this patch applied the problem has not been observed and the board
> has managed above 250 boot loops.
> 
> The AT91SAM9260 datasheet tells us that with the instruction cache
> disabled all instructions are fetched from SDRAM. And we have an errata
> telling us we must power down the SDRAM before issuing cpu reset.
> 
> This means we need the instruction cache enabled in at91sam9260_reset()
> At the moment it is being disabled in cpu_proc_fin() which is called from
> arch/arm/kernel/reboot.c.

Are you using kexec reboot or implemented hibernate mode on this machine?
I'm seeing cpu_proc_fin() is called only in case of kexec reboot or
switching to hibernate mode.

In case of normal reboot (e.g. reboot command) machine_restart() from
arch/arm/kernel/reboot.c is called. Please correct me if I'm wrong.

Thank you,
Claudiu Beznea

> 
> Signed-off-by: Jonas Danielsson <jonas@...ital-systems.com>
> ---
>  drivers/power/reset/at91-reset.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/power/reset/at91-reset.c b/drivers/power/reset/at91-reset.c
> index f44a9ffcc2ab..78972bba64df 100644
> --- a/drivers/power/reset/at91-reset.c
> +++ b/drivers/power/reset/at91-reset.c
> @@ -50,14 +50,24 @@ static void __iomem *at91_ramc_base[2], *at91_rstc_base;
>  static struct clk *sclk;
>  
>  /*
> -* unless the SDRAM is cleanly shutdown before we hit the
> +* Errata 43.1.7.1 RSTC: Reset during SDRAM Accesses
> +*
> +* Unless the SDRAM is cleanly shutdown before we hit the
>  * reset register it can be left driving the data bus and
>  * killing the chance of a subsequent boot from NAND
> +*
> +* Since we are disabling SDRAM need to make sure that the
> +* instruction cache is enabled.
>  */
>  static int at91sam9260_restart(struct notifier_block *this, unsigned long mode,
>  			       void *cmd)
>  {
>  	asm volatile(
> +		/* Enable I-cache */
> +		"mrc	p15, 0, r0, c1, c0, 0\n\t"
> +		"orr	r0, r0, #4096\n\t" /* CR_I (bit 12) */
> +		"mcr	p15, 0, r0, c1, c0, 0\n\t"
> +
>  		/* Align to cache lines */
>  		".balign 32\n\t"
>  
>