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

[Rob Herring <robh@kernel.org>]

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@bootlin.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@bootlin.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@crapouillou.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.

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

Rob