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Date: Fri, 16 Jul 2021 01:48:20 +0000
From: Billy Tsai <billy_tsai@...eedtech.com>
To: Uwe Kleine-König
<u.kleine-koenig@...gutronix.de>
CC: "lee.jones@...aro.org" <lee.jones@...aro.org>,
"robh+dt@...nel.org" <robh+dt@...nel.org>,
"joel@....id.au" <joel@....id.au>,
"andrew@...id.au" <andrew@...id.au>,
"thierry.reding@...il.com" <thierry.reding@...il.com>,
"p.zabel@...gutronix.de" <p.zabel@...gutronix.de>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-pwm@...r.kernel.org" <linux-pwm@...r.kernel.org>,
BMC-SW <BMC-SW@...eedtech.com>
Subject: Re: [v9 2/2] pwm: Add Aspeed ast2600 PWM support
Hello Uwe Kleine-König,
On 2021/7/15, 11:06 PM, "Uwe Kleine-König" <u.kleine-koenig@...gutronix.de>> wrote:
On Fri, Jul 09, 2021 at 02:52:17PM +0800, Billy Tsai wrote:
>> This patch add the support of PWM controller which can be found at aspeed
>> ast2600 soc. The pwm supoorts up to 16 channels and it's part function
>> of multi-function device "pwm-tach controller".
>>
>> Signed-off-by: Billy Tsai <billy_tsai@...eedtech.com>
>> ---
>> drivers/pwm/Kconfig | 9 +
>> drivers/pwm/Makefile | 1 +
>> drivers/pwm/pwm-aspeed-ast2600.c | 316 +++++++++++++++++++++++++++++++
>> 3 files changed, 326 insertions(+)
>> create mode 100644 drivers/pwm/pwm-aspeed-ast2600.c
>>
>> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
>> index 63be5362fd3a..a5aac3ca4ac7 100644
>> --- a/drivers/pwm/Kconfig
>> +++ b/drivers/pwm/Kconfig
>> @@ -51,6 +51,15 @@ config PWM_AB8500
>> To compile this driver as a module, choose M here: the module
>> will be called pwm-ab8500.
>>
>> +config PWM_ASPEED_AST2600
>> + tristate "Aspeed ast2600 PWM support"
>> + depends on ARCH_ASPEED || COMPILE_TEST
> I think you need
> depdens on HAVE_CLK && HAS_IOMEM
> here.
Ok, I will add it to next version.
>> + help
>> + This driver provides support for Aspeed ast2600 PWM controllers.
>> +
>> + To compile this driver as a module, choose M here: the module
>> + will be called pwm-aspeed-ast2600.
>> +
>> config PWM_ATMEL
>> tristate "Atmel PWM support"
>> depends on OF
>> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
>> index cbdcd55d69ee..ada454f9129a 100644
>> --- a/drivers/pwm/Makefile
>> +++ b/drivers/pwm/Makefile
>> @@ -2,6 +2,7 @@
>> obj-$(CONFIG_PWM) += core.o
>> obj-$(CONFIG_PWM_SYSFS) += sysfs.o
>> obj-$(CONFIG_PWM_AB8500) += pwm-ab8500.o
>> +obj-$(CONFIG_PWM_ASPEED_AST2600) += pwm-aspeed-ast2600.o
>> obj-$(CONFIG_PWM_ATMEL) += pwm-atmel.o
>> obj-$(CONFIG_PWM_ATMEL_HLCDC_PWM) += pwm-atmel-hlcdc.o
>> obj-$(CONFIG_PWM_ATMEL_TCB) += pwm-atmel-tcb.o
>> diff --git a/drivers/pwm/pwm-aspeed-ast2600.c b/drivers/pwm/pwm-aspeed-ast2600.c
>> new file mode 100644
>> index 000000000000..68a45ba3b32b
>> --- /dev/null
>> +++ b/drivers/pwm/pwm-aspeed-ast2600.c
>> @@ -0,0 +1,316 @@
>> +// SPDX-License-Identifier: GPL-2.0-or-later
>> +/*
>> + * Copyright (C) 2021 Aspeed Technology Inc.
>> + *
>> + * PWM controller driver for Aspeed ast2600 SoCs.
>> + * This drivers doesn't support earlier version of the IP.
>> + *
>> + * The formula of pwm period duration:
>> + * period duration = ((DIV_L + 1) * (PERIOD + 1) << DIV_H) / input-clk
>> + *
>> + * The formula of pwm duty cycle duration:
>> + * duty cycle duration = period duration * DUTY_CYCLE_FALLING_POINT / (PERIOD + 1)
>> + * = ((DIV_L + 1) * DUTY_CYCLE_FALLING_POINT << DIV_H) / input-clk
>> + *
>> + * The software driver fixes the period to 255, which causes the high-frequency
>> + * precision of the PWM to be coarse, in exchange for the fineness of the duty cycle.
>> + *
>> + * Register usage:
>> + * PIN_ENABLE: When it is unset the pwm controller will always output low to the extern.
>> + * Use to determine whether the PWM channel is enabled or disabled
>> + * CLK_ENABLE: When it is unset the pwm controller will reset the duty counter to 0 and
>> + * output low to the PIN_ENABLE mux after that the driver can still change the pwm period
>> + * and duty and the value will apply when CLK_ENABLE be set again.
>> + * Use to determine whether duty_cycle bigger than 0.
>> + * PWM_ASPEED_CTRL_INVERSE: When it is toggled the output value will inverse immediately.
>> + * PWM_ASPEED_DUTY_CYCLE_FALLING_POINT/PWM_ASPEED_DUTY_CYCLE_RISING_POINT: When these two
>> + * values are equal it means the duty cycle = 100%.
>> + *
>> + * Limitations:
>> + * - When changing both duty cycle and period, we cannot prevent in
>> + * software that the output might produce a period with mixed
>> + * settings.
>> + * - Disabling the PWM doesn't complete the current period.
> Another is: The PWM doesn't support duty_cycle 0, on such a request the
> PWM is disabled which results in a constant inactive level.
> (This is correct, is it? Or does it yield a constant 0 level?)
Our pwm can support duty_cycle 0 by unset CLK_ENABLE.
Other naming suggestion I will fix in the next version.
Thanks
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