linux-kernel - Re: [PATCH v5] atmel_flexcom: Support backup mode

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Message-ID: <CAGkQfmMK_a5+zyyoHZsnfvNuxmNLeM0t40MrbPMMwKcNXDZTFA@mail.gmail.com>
Date:   Mon, 23 Oct 2017 19:03:08 +0200
From:   Romain Izard <romain.izard.pro@...il.com>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v5] atmel_flexcom: Support backup mode

2017-10-23 18:07 GMT+02:00 Lee Jones <lee.jones@...aro.org>:
> On Mon, 23 Oct 2017, Lee Jones wrote:
>> On Thu, 19 Oct 2017, Romain Izard wrote:
>>
>> > The controller used by a flexcom module is configured at boot, and left
>> > alone after this. As the configuration will be lost after backup mode,
>> > restore the state of the flexcom driver on resume.
>> >
>> > Signed-off-by: Romain Izard <romain.izard.pro@...il.com>
>> > Acked-by: Nicolas Ferre <nicolas.ferre@...rochip.com>
>> > Tested-by: Nicolas Ferre <nicolas.ferre@...rochip.com>
>> > ---
>> > Changes in v5:
>> > * extract from the patch series, and send as a standalone patch
>> >
>> >  drivers/mfd/atmel-flexcom.c | 65 ++++++++++++++++++++++++++++++++++-----------
>> >  1 file changed, 50 insertions(+), 15 deletions(-)
>> >
>> > diff --git a/drivers/mfd/atmel-flexcom.c b/drivers/mfd/atmel-flexcom.c
>> > index 064bde9cff5a..ef1235c4a179 100644
>> > --- a/drivers/mfd/atmel-flexcom.c
>> > +++ b/drivers/mfd/atmel-flexcom.c
>> > @@ -39,34 +39,44 @@
>> >  #define FLEX_MR_OPMODE(opmode)     (((opmode) << FLEX_MR_OPMODE_OFFSET) &  \
>> >                              FLEX_MR_OPMODE_MASK)
>> >
>> > +struct atmel_flexcom {
>> > +   void __iomem *base;
>> > +   u32 opmode;
>> > +   struct clk *clk;
>> > +};
>> >
>> >  static int atmel_flexcom_probe(struct platform_device *pdev)
>> >  {
>> >     struct device_node *np = pdev->dev.of_node;
>> > -   struct clk *clk;
>> >     struct resource *res;
>> > -   void __iomem *base;
>> > -   u32 opmode;
>> > +   struct atmel_flexcom *afc;
>>
>> Nit: I'd prefer if you call this 'ddata'.
>>
>> But the concept and implementation is fine, so if you're going to
>> change it please do so and apply my:
>>
>> Acked-by: Lee Jones <lee.jones@...aro.org>
>
> Also, 'back-up mode' isn't really a thing is it?
>
> How about "Reinstall state on resume" or similar?
>

The expression comes from the SAMA5D2's datasheet.

Other Atmel chips use a different single suspend mode with Linux, where
the SoC remains completely powered with a slow clock. The registers are
preserved in this mode, so there is no need for a specific suspend and
resume code.

The SoC can also be powered down, but the CPU is reset and only a small
part is powered with a backup battery to maintain a valid RTC and a
small internal SRAM.

In the SAMA5D2, the mode with only the backup power supply has been
extended to isolate the memory I/O lines, making it possible to keep the
external SDRAM memory in self-refresh. This mode has a lower consumption
compared to the slow clock mode, but it has a higher wakeup latency, and
needs specific software support in the bootloader and the kernel.

As a result, the "backup mode" expression is used to contrast with the
"slow clock" expression when describing the different suspend modes
supported by the chip.

But if you think that it is necessary, I can reword the commit.

Best regards,
-- 
Romain Izard