From: Baruch Siach <baruch@tkos.co.il>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Thierry Reding <thierry.reding@gmail.com>,
Lee Jones <lee.jones@linaro.org>, Andy Gross <agross@kernel.org>,
Bjorn Andersson <bjorn.andersson@linaro.org>,
Balaji Prakash J <bjagadee@codeaurora.org>,
Rob Herring <robh+dt@kernel.org>,
Robert Marko <robert.marko@sartura.hr>,
devicetree@vger.kernel.org, linux-arm-msm@vger.kernel.org,
linux-arm-kernel@lists.infradead.org, linux-pwm@vger.kernel.org
Subject: Re: [PATCH 1/3] pwm: driver for qualcomm ipq6018 pwm block
Date: Sun, 23 May 2021 18:54:08 +0300 [thread overview]
Message-ID: <87zgwltpi7.fsf@tarshish> (raw)
In-Reply-To: <20210522213524.lnb5bds5hvv2f2zi@pengutronix.de>
Hi Uwe,
Thanks for your review comments.
On Sun, May 23 2021, Uwe Kleine-König wrote:
> On Wed, May 19, 2021 at 10:48:44AM +0300, Baruch Siach wrote:
>> Driver for the PWM block in Qualcomm IPQ6018 line of SoCs. Based on
>> driver from downstream Codeaurora kernel tree. Removed support for older
>> (V1) variants because I have no access to that hardware.
>>
>> Tested on IPQ6010 based hardware.
>>
>> Signed-off-by: Baruch Siach <baruch@tkos.co.il>
[...]
>> +static void ipq_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
>> +{
>> + struct ipq_pwm_chip *ipq_chip = to_ipq_pwm_chip(pwm->chip);
>> + unsigned offset = ipq_pwm_reg_offset(pwm, PWM_CFG_REG1);
>> + unsigned long val;
>> +
>> + val = readl(ipq_chip->mem + offset);
>> + val |= PWM_UPDATE;
>
> What is the effect of this register bit?
>
> Does the output become inactive or does it freeze at state that happens
> to be emitted when the ENABLE bit is removed?
I don't know. PWM does not work when this bit is not set here. The
original downstream driver[1] does not set this bit on disable. But it
also enables PWM unconditionally on .config. I added the 'enabled' check
in .config, and then PWM stopped working even when enabled later. It was
only by accident (excess copy/paste) that I found this workaround.
A comment on the original code says that PWM_UPDATE is "auto cleared".
This is evidently not true on my hardware (IPQ6010). This might be true
for older variants of this PWM block. Unfortunately, I have no access to
hardware documentation.
[1] https://source.codeaurora.org/quic/qsdk/oss/kernel/linux-ipq-5.4/tree/drivers/pwm/pwm-ipq.c?h=NHSS.QSDK.11.4.1.r1&id=9e4627b7088b0c06ddd910c8770274d26613de9e
baruch
--
~. .~ Tk Open Systems
=}------------------------------------------------ooO--U--Ooo------------{=
- baruch@tkos.co.il - tel: +972.52.368.4656, http://www.tkos.co.il -
next prev parent reply other threads:[~2021-05-23 15:54 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-19 7:48 [PATCH 1/3] pwm: driver for qualcomm ipq6018 pwm block Baruch Siach
2021-05-19 7:48 ` [PATCH 2/3] dt-bindings: pwm: add IPQ6018 binding Baruch Siach
2021-05-21 1:34 ` Rob Herring
2021-05-19 7:48 ` [PATCH 3/3] arm64: dts: ipq6018: add pwm node Baruch Siach
2021-05-22 21:35 ` [PATCH 1/3] pwm: driver for qualcomm ipq6018 pwm block Uwe Kleine-König
2021-05-23 15:54 ` Baruch Siach [this message]
2021-05-22 21:37 ` Uwe Kleine-König
2022-02-07 9:30 Baruch Siach
2023-09-15 6:25 ` Devi Priya
2023-09-15 6:36 ` Baruch Siach
2023-09-20 4:58 ` Devi Priya
2023-09-22 6:00 ` Devi Priya
2023-09-22 8:35 ` Baruch Siach
2023-09-22 10:56 ` Devi Priya
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