Re: [PATCH 4.4 23/26] power: reset: at91-poweroff: timely shutdown LPDDR memories

Alexandre Belloni
2017-04-06T18:13:41Z

On 06/04/2017 at 18:45:39 +0100, Ben Hutchings wrote:
> On Thu, 2017-04-06 at 10:38 +0200, Greg Kroah-Hartman wrote:
> > 4.4-stable review patch. If anyone has any objections, please let me know.
> >
> > ------------------
> >
> > From: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> >
> > commit 0b0408745e7ff24757cbfd571d69026c0ddb803c upstream.
> >
> > LPDDR memories can only handle up to 400 uncontrolled power off. Ensure the
> > proper power off sequence is used before shutting down the platform.
> >
> > Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
> > Signed-off-by: Sebastian Reichel <sre@kernel.org>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> [...]
> > +static void at91_lpddr_poweroff(void)
> > +{
> > + asm volatile(
> > + /* Align to cache lines */
> > + ".balign 32\n\t"
> > +
> > + /* Ensure AT91_SHDW_CR is in the TLB by reading it */
> > + " ldr r6, [%2, #" __stringify(AT91_SHDW_CR) "]\n\t"
>
> This clobbers r6...
>
> > + /* Power down SDRAM0 */
> > + " str %1, [%0, #" __stringify(AT91_DDRSDRC_LPR) "]\n\t"
> > + /* Shutdown CPU */
> > + " str %3, [%2, #" __stringify(AT91_SHDW_CR) "]\n\t"
> > +
> > + " b .\n\t"
> > + :
> > + : "r" (mpddrc_base),
> > + "r" cpu_to_le32(AT91_DDRSDRC_LPDDR2_PWOFF),
> > + "r" (at91_shdwc_base),
> > + "r" cpu_to_le32(AT91_SHDW_KEY | AT91_SHDW_SHDW)
> > + : "r0");
> [...]
>
> ...but the clobber list has r0.
>

Indeed. However, It doesn't matter much as nothing can possibly run
afterwards.

--
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering