linux-kernel - Re: [PATCH] rtc: jz4740: Add support for the JZ4725B, JZ4760, JZ4770

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Date:   Fri, 20 Jul 2018 21:03:59 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Rob Herring <robh@...nel.org>
Cc:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Mark Rutland <mark.rutland@....com>, linux-rtc@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] rtc: jz4740: Add support for the JZ4725B, JZ4760, JZ4770

Hi,

Le ven. 20 juil. 2018 à 17:39, Rob Herring <robh@...nel.org> a écrit :
> On Sat, Jul 14, 2018 at 03:50:08PM +0200, Paul Cercueil wrote:
>> 
>> 
>>  Le sam. 14 juil. 2018 à 15:32, Alexandre Belloni
>>  <alexandre.belloni@...tlin.com> a écrit :
>>  > On 14/07/2018 15:25:33+0200, Paul Cercueil wrote:
>>  > >  Hi Alexandre,
>>  > >
>>  > >  Le sam. 14 juil. 2018 à 15:19, Alexandre Belloni
>>  > >  <alexandre.belloni@...tlin.com> a écrit :
>>  > >  > Hello,
>>  > >  >
>>  > >  > On 13/07/2018 17:14:24+0200, Paul Cercueil wrote:
>>  > >  > >  The RTC in the JZ4725B works just like the one in the 
>> JZ4740.
>>  > >  > >
>>  > >  > >  The RTC in the JZ4760 and JZ4770 work just like the one 
>> in the
>>  > >  > > JZ4780.
>>  > >  > >
>>  > >  > >  Signed-off-by: Paul Cercueil <paul@...pouillou.net>
>>  > >  > >  ---
>>  > >  > >   
>> Documentation/devicetree/bindings/rtc/ingenic,jz4740-rtc.txt
>>  > > |  3
>>  > >  > > +++
>>  > >  > >   drivers/rtc/rtc-jz4740.c
>>  > > | 11
>>  > >  > > ++++++++++-
>>  > >  > >   2 files changed, 13 insertions(+), 1 deletion(-)
>>  > >  > >
>>  > >  > >  diff --git
>>  > >  > > 
>> a/Documentation/devicetree/bindings/rtc/ingenic,jz4740-rtc.txt
>>  > >  > > 
>> b/Documentation/devicetree/bindings/rtc/ingenic,jz4740-rtc.txt
>>  > >  > >  index 41c7ae18fd7b..a9e821de84f2 100644
>>  > >  > >  ---
>>  > > a/Documentation/devicetree/bindings/rtc/ingenic,jz4740-rtc.txt
>>  > >  > >  +++
>>  > > b/Documentation/devicetree/bindings/rtc/ingenic,jz4740-rtc.txt
>>  > >  > >  @@ -4,6 +4,9 @@ Required properties:
>>  > >  > >
>>  > >  > >   - compatible: One of:
>>  > >  > >     - "ingenic,jz4740-rtc" - for use with the JZ4740 SoC
>>  > >  > >  +  - "ingenic,jz4725b-rtc" - for use with the JZ4725B SoC
>>  > >  > >  +  - "ingenic,jz4760-rtc" - for use with the JZ4760 SoC
>>  > >  > >  +  - "ingenic,jz4770-rtc" - for use with the JZ4770 SoC
>>  > >  > >     - "ingenic,jz4780-rtc" - for use with the JZ4780 SoC
>>  > >  > >   - reg: Address range of rtc register set
>>  > >  > >   - interrupts: IRQ number for the alarm interrupt
>>  > >  > >  diff --git a/drivers/rtc/rtc-jz4740.c
>>  > > b/drivers/rtc/rtc-jz4740.c
>>  > >  > >  index d0a891777f44..1c867e3a0ea5 100644
>>  > >  > >  --- a/drivers/rtc/rtc-jz4740.c
>>  > >  > >  +++ b/drivers/rtc/rtc-jz4740.c
>>  > >  > >  @@ -54,6 +54,9 @@
>>  > >  > >
>>  > >  > >   enum jz4740_rtc_type {
>>  > >  > >   	ID_JZ4740,
>>  > >  > >  +	ID_JZ4725B,
>>  > >  > >  +	ID_JZ4760,
>>  > >  > >  +	ID_JZ4770,
>>  > >  >
>>  > >  > I wouldn't introduce those ids unless there are handling
>>  > > differences at
>>  > >  > some point.
>>  > >
>>  > >  Well there are handling differences, see below.
>>  > >
>>  > >  > >   	ID_JZ4780,
>>  > >  > >   };
>>  > >  > >
>>  > >  > >  @@ -114,7 +117,7 @@ static inline int
>>  > > jz4740_rtc_reg_write(struct
>>  > >  > > jz4740_rtc *rtc, size_t reg,
>>  > >  > >   {
>>  > >  > >   	int ret = 0;
>>  > >  > >
>>  > >  > >  -	if (rtc->type >= ID_JZ4780)
>>  > >  > >  +	if (rtc->type >= ID_JZ4760)
>>  > >  >
>>  > >  > This would avoid that change (and the test would preferably 
>> be
>>  > >  > (rtc->type == ID_JZ4780))
>>  > >
>>  > >  That branch should be taken if the SoC is JZ4760, JZ4770 or 
>> JZ4780.
>>  > >  It should not be taken if the SoC is JZ4740 or JZ4725B.
>>  >
>>  > Sure but you can achieve that with only 2 ids...
>>  >
>>  > >
>>  > >  > >   		ret = jz4780_rtc_enable_write(rtc);
>>  > >  > >   	if (ret == 0)
>>  > >  > >   		ret = jz4740_rtc_wait_write_ready(rtc);
>>  > >  > >  @@ -300,6 +303,9 @@ static void jz4740_rtc_power_off(void)
>>  > >  > >
>>  > >  > >   static const struct of_device_id jz4740_rtc_of_match[] = 
>> {
>>  > >  > >   	{ .compatible = "ingenic,jz4740-rtc", .data = (void
>>  > > *)ID_JZ4740 },
>>  > >  > >  +	{ .compatible = "ingenic,jz4725b-rtc", .data = (void
>>  > > *)ID_JZ4725B
>>  > >  > > },
>>  > >  > >  +	{ .compatible = "ingenic,jz4760-rtc", .data = (void
>>  > > *)ID_JZ4760 },
>>  > >  > >  +	{ .compatible = "ingenic,jz4770-rtc", .data = (void
>>  > > *)ID_JZ4770 },
>>  >
>>  > By doing the correct mapping here e.g:
>>  >
>>  > { .compatible = "ingenic,jz4725b-rtc", .data = (void *)ID_JZ4740 
>> },
>> 
>>  Not very pretty and future-proof if you ask me...
> 
> Looks to me like this can be handled entirely in DT without driver
> changes like the other patches. Correct usage of compatible strings is
> what gives you future-proofing. And no driver change is better than
> needless changing.

If I make e.g. the jz4760 and jz4770 use the jz4780 compatible string, 
but
then I want to implement a new feature that only exists on the jz4780, 
how
can I do it without breaking everything?

> It may look a bit wierd if 4780 is the fallback for 4770, but if the
> 4780 is older, then that actually makes sense.

The 4770 is older than the 4780.

Thanks,
-Paul