netdev - Re: [PATCH 17/21] power: reset: at91-poweroff: lookup for proper pmc dt node for sam9x7

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Date: Fri, 16 Jun 2023 17:32:30 +0000
From: <Varshini.Rajendran@...rochip.com>
To: <conor@...nel.org>, <Nicolas.Ferre@...rochip.com>
CC: <krzysztof.kozlowski@...aro.org>, <tglx@...utronix.de>, <maz@...nel.org>,
	<robh+dt@...nel.org>, <krzysztof.kozlowski+dt@...aro.org>,
	<conor+dt@...nel.org>, <alexandre.belloni@...tlin.com>,
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	<linux-pm@...r.kernel.org>, <Hari.PrasathGE@...rochip.com>,
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	<Manikandan.M@...rochip.com>, <Dharma.B@...rochip.com>,
	<Nayabbasha.Sayed@...rochip.com>, <Balakrishnan.S@...rochip.com>
Subject: Re: [PATCH 17/21] power: reset: at91-poweroff: lookup for proper pmc
 dt node for sam9x7

On 05/06/23 6:56 pm, Conor Dooley wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> Hey,
> 
> On Mon, Jun 05, 2023 at 03:04:34PM +0200, Nicolas Ferre wrote:
>> On 05/06/2023 at 08:43, Krzysztof Kozlowski wrote:
>>> On 03/06/2023 22:02, Varshini Rajendran wrote:
>>>> Use sam9x7 pmc's compatible to lookup for in the SHDWC driver
>>>>
>>>> Signed-off-by: Varshini Rajendran <varshini.rajendran@...rochip.com>
>>>> ---
>>>>   drivers/power/reset/at91-sama5d2_shdwc.c | 1 +
>>>>   1 file changed, 1 insertion(+)
>>>>
>>>> diff --git a/drivers/power/reset/at91-sama5d2_shdwc.c b/drivers/power/reset/at91-sama5d2_shdwc.c
>>>> index d8ecffe72f16..d0f29b99f25e 100644
>>>> --- a/drivers/power/reset/at91-sama5d2_shdwc.c
>>>> +++ b/drivers/power/reset/at91-sama5d2_shdwc.c
>>>> @@ -326,6 +326,7 @@ static const struct of_device_id at91_pmc_ids[] = {
>>>>        { .compatible = "atmel,sama5d2-pmc" },
>>>>        { .compatible = "microchip,sam9x60-pmc" },
>>>>        { .compatible = "microchip,sama7g5-pmc" },
>>>> +     { .compatible = "microchip,sam9x7-pmc" },
>>>
>>> Why do you need new entry if these are compatible?
>>
>> Yes, PMC is very specific to a SoC silicon. As we must look for it in the
>> shutdown controller, I think we need a new entry here.
> 
> Copy-pasting this for a wee bit of context as I have two questions.
> 
> | static const struct of_device_id at91_shdwc_of_match[] = {
> | 	{
> | 		.compatible = "atmel,sama5d2-shdwc",
> | 		.data = &sama5d2_reg_config,
> | 	},
> | 	{
> | 		.compatible = "microchip,sam9x60-shdwc",
> | 		.data = &sam9x60_reg_config,
> | 	},
> | 	{
> | 		.compatible = "microchip,sama7g5-shdwc",
> | 		.data = &sama7g5_reg_config,
> | 	}, {
> | 		/*sentinel*/
> | 	}
> | };
> | MODULE_DEVICE_TABLE(of, at91_shdwc_of_match);
> | 
> | static const struct of_device_id at91_pmc_ids[] = {
> | 	{ .compatible = "atmel,sama5d2-pmc" },
> | 	{ .compatible = "microchip,sam9x60-pmc" },
> | 	{ .compatible = "microchip,sama7g5-pmc" },
> | 	{ .compatible = "microchip,sam9x7-pmc" },
> | 	{ /* Sentinel. */ }
> | };
> 
> If there's no changes made to the code, other than adding an entry to
> the list of pmc compatibles, then either this has the same as an
> existing SoC, or there is a bug in the patch, since the behaviour of
> the driver will not have changed.
> 
> Secondly, this patch only updates the at91_pmc_ids and the dts patch
> contains:
> | shutdown_controller: shdwc@...ffe10 {
> | 	compatible = "microchip,sam9x60-shdwc";
> | 	reg = <0xfffffe10 0x10>;
> | 	clocks = <&clk32k 0>;
> | 	#address-cells = <1>;
> | 	#size-cells = <0>;
> | 	atmel,wakeup-rtc-timer;
> | 	atmel,wakeup-rtt-timer;
> | 	status = "disabled";
> | };
> 
> ...which would mean that the there's nothing different between the
> programming models for the sam9x60 and sam9x7. If that's the case, the
> dt-binding & dts should list the sam9x60 as a fallback for the sam9x7 &
> there is no change required to the driver. If it's not the case, then
> there's a bug in this patch and the dts one 😄
> 
> In general, if things are the same as previous products, there's no need
> to change the drivers at all & just add fallback compatibles to the
> bindings and dts. IFF some difference pops up in the future, then the
> sam9x7 compatible will already exist in the dts, and can then be added
> to the driver.

Yes. I totally agree with you. In this patch I have not added a 
compatible for the shutdown controller for sam9x7. I have added the 
compatible of the pmc used in sam9x7 in the list of compatibles to use 
the right pmc driver in order to control the clk disable functions for 
the right pmc. The shutdown programming is no different, so no new 
compatible for sam9x7 (like microchip,sam9x7-shdwc). But the PMC is 
totally different than the other older SoCs, hence I have added the new 
compatible microchip,sam9x7-pmc in the list as it is defined in the 
drivers/clk/at91/sam9x7.c driver. Hope this is clear.

> 
> Cheers,
> Conor.
> 

-- 
Thanks and Regards,
Varshini Rajendran.