linux-kernel - Re: [PATCH] rtc: omap: Support scratch registers

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Message-ID: <20171108082145.kpd3c45x5skce5wd@piout.net>
Date:   Wed, 8 Nov 2017 09:21:45 +0100
From:   Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:     Keerthy <j-keerthy@...com>
Cc:     Sekhar Nori <nsekhar@...com>, linux-rtc@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Linux OMAP List <linux-omap@...r.kernel.org>
Subject: Re: [PATCH] rtc: omap: Support scratch registers

On 08/11/2017 at 13:36:15 +0530, Keerthy wrote:
> 
> 
> On Wednesday 08 November 2017 12:46 PM, Alexandre Belloni wrote:
> > On 08/11/2017 at 12:38:05 +0530, Keerthy wrote:
> >>
> >>
> >> On Wednesday 08 November 2017 11:57 AM, Alexandre Belloni wrote:
> >>> Hi,
> >>>
> >>> On 08/11/2017 at 11:30:45 +0530, Keerthy wrote:
> >>>>>>> +static int omap_rtc_scratch_read(void *priv, unsigned int offset, void *_val,
> >>>>>>> +				 size_t bytes)
> >>>>>>> +{
> >>>>>>> +	struct omap_rtc	*rtc = priv;
> >>>>>>> +	u32 *val = _val;
> >>>>>>> +	int i;
> >>>>>>> +
> >>>>>>> +	for (i = 0; i < bytes / 4; i++)
> >>>>>>> +		val[i] = rtc_readl(rtc,
> >>>>>>> +				   OMAP_RTC_SCRATCH0_REG + offset + (i * 4));
> >>>>
> >>>> Can the offset be the Scratch register number instead of bytes offset?
> >>>> More intuitive to me.
> >>>>
> >>>> So that one can request using offset as 0, 1, 2 instead of 0, 4, 8?
> >>>>
> >>>
> >>> Well, the offset is coming from the nvmem core, itself getting it from
> >>> the Linux file API (and it is in bytes). However, you have the guarantee
> >>> that it will be aligned on a word, see:
> >>> http://elixir.free-electrons.com/linux/latest/source/drivers/nvmem/core.c#L88
> >>
> >> Okay Alexandre. Thanks for clarifying. Looks good to me.
> >> I have tested on AM437X-GP-EVM.
> >>
> > 
> > If needed, you can define nvmem cells (and I guess that is what you
> > want):
> > http://elixir.free-electrons.com/linux/latest/source/Documentation/devicetree/bindings/nvmem/nvmem.txt
> 
> With this patch we cannot still use nvmem_device_write and
> nvmem_device_read as the nvmem_device is still not registered.
> 
> How can a driver write to scratch pad registers? Should we be calling
> nvmem_register in the probe?

It is not needed, it is registered by rtc_nvmem_register().

nvmem_device_read/write are working because that is what I'm using to
implement the old sysfs ABI with rtc_nvram_read/write.

-- 
Alexandre Belloni, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com