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

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Message-ID: <20171108083533.5ibx43biwk7exlnc@piout.net>
Date:   Wed, 8 Nov 2017 09:35:33 +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 14:02:31 +0530, Keerthy wrote:
> 
> 
> On Wednesday 08 November 2017 02:01 PM, Keerthy wrote:
> > 
> > 
> > On Wednesday 08 November 2017 01:51 PM, Alexandre Belloni wrote:
> >> 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().
> > 
> > Let me go through the chain:
> > 
> > rtc_register_device -> __rtc_register_device --> rtc_nvmem_register ->
> > rtc_nvram_register
> > 
> > I am seeing that for rtc-omap driver there is rtc_register_device call
> 
> I mean there NO rtc_register_device call.
> 
> > and i see that rtc_nvmem_register is not getting called.
> > 
> > Should we add rtc_register_device in probe of rtc-omap?
> > 

Do you also have that patch:
https://git.kernel.org/pub/scm/linux/kernel/git/abelloni/linux.git/commit/?h=rtc-next&id=57072758623fa4f3019bce65e2b00f24af8dfdd7

?

> >>
> >> 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