linux-kernel - Re: [PATCH v3 3/8] arm64: dts: ls1028a: add flextimer based pwm nodes

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Date:   Tue, 16 Aug 2022 11:04:18 +0200
From:   Michael Walle <michael@...le.cc>
To:     biwen.li@....com
Cc:     leoyang.li@....com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, olteanv@...il.com,
        shawnguo@...nel.org
Subject: Re: [PATCH v3 3/8] arm64: dts: ls1028a: add flextimer based pwm nodes

Am 2022-07-28 11:33, schrieb Michael Walle:
> Hi,
> 
> sorry for digging up this old thread. But I've noticed some
> inconsistencies here while syncing the device tree with u-boot.
> 
>>> On Wed, Apr 13, 2022 at 06:07:20PM +0000, Leo Li wrote:
>>> > > arch/arm64/boot/dts/freescale/fsl-ls1028a.dtsi:1210.21-1219.5:
>>> > > Warning
>>> > > (unique_unit_address): /soc/pwm@...0000: duplicate unit-address
>>> > > (also used in node /soc/timer@...0000)
>>> > > arch/arm64/boot/dts/freescale/fsl-ls1028a.dtsi:1221.21-1230.5:
>>> > > Warning
>>> > > (unique_unit_address): /soc/pwm@...0000: duplicate unit-address
>>> > > (also used in node /soc/timer@...0000)
>>> >
>>> > Well, this is similar situation as pcie.  The flextimer controller can
>>> > be used as timer, PWM or alarm.  We have separate drivers and bindings
>>> > for these modes which resulted in different nodes for the same
>>> > controller.
>>> 
>>> I think the mfd framework can address the situation where multiple 
>>> drivers,
>>> with multiple functionalities, want access to the same memory region?
>> 
>> I know mfd is used for device providing multiple functions at the same
>> time. I'm not sure if it can help dealing with the one function at a 
>> time
>> scenario.
> 
> Funnily enough, I had the same concern:
> https://lore.kernel.org/lkml/92eaa24876a823aa5833435f51095812@walle.cc/
> 
> Anyway, I have a few questions about the device tree here:
> 
>> +	rtc_clk: rtc-clk {
>> +		compatible = "fixed-clock";
>> +		#clock-cells = <0>;
>> +		clock-frequency = <32768>;
>> +		clock-output-names = "rtc_clk";
>> +	};
>> +
> 
> Is that an internal clock? I've checked the RDB schematics and the
> RTC clock output is not connected to anything. The RM of the LS1028A
> mentions the fixed clock input of the flex timer, but it doesn't say
> where it is connected to. It just says there is no 
> "internally-generated
> secure clock" support on any of the timer modules.
> 
> In ch19.3 it also says "For the chip-specific implementation details of
> this module's instances, see the chip configuration information". But
> I'm not sure where to find this.
> 
> 
>> +		pwm0: pwm@...0000 {
>> +			compatible = "fsl,vf610-ftm-pwm";
>> +			#pwm-cells = <3>;
>> +			reg = <0x0 0x2800000 0x0 0x10000>;
>> +			clock-names = "ftm_sys", "ftm_ext",
>> +				      "ftm_fix", "ftm_cnt_clk_en";
>> +			clocks = <&clockgen 4 1>, <&clockgen 4 1>,
>> +				 <&rtc_clk>, <&clockgen 4 1>;
> 
> ftm_ext seems to be the (optional) external clock, eg FTMn_EXTCLK. Why 
> is
> it connected to <&clockgen 4 1>? That doesn't make sense. The driver
> itself, won't probe if the clock isn't there either and assumes that 
> the
> external clock is always there. That seems wrong, too.
> 
> Can you shed some light on this?

Ping.

-michael