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

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Message-ID: <20171024083742.j7zlfj2drd4nzetm@dell>
Date:   Tue, 24 Oct 2017 09:37:42 +0100
From:   Lee Jones <lee.jones@...aro.org>
To:     Romain Izard <romain.izard.pro@...il.com>
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

On Mon, 23 Oct 2017, Romain Izard wrote:

> 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.

No, no need.  Thanks for the excellent explanation.

It might be worth you providing a succinct description of the
datasheet's meaning of "back-up mode" though.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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