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

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Message-ID: <6e511121-d713-2056-f8f9-6cdd668a7598@ti.com>
Date:   Wed, 8 Nov 2017 14:18:35 +0530
From:   Keerthy <j-keerthy@...com>
To:     Alexandre Belloni <alexandre.belloni@...e-electrons.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 Wednesday 08 November 2017 02:05 PM, Alexandre Belloni wrote:
> 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
> 
> ?

Ah! Now everything falls in place :-). I did not receive this patch. I
believe i need to add a patch so linux-omap list gets Cc'd whenever
rtc-omap driver is touched.

Thanks a bunch!

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