linux-kernel - Re: [PATCH v2 2/3] hwmon: (aspeed-pwm-tacho) Deassert reset in probe

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Date:   Thu, 2 Nov 2017 07:54:06 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Joel Stanley <joel@....id.au>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Philipp Zabel <philipp.zabel@...il.com>,
        Mykola Kostenok <c_mykolak@...lanox.com>,
        Jaghathiswari Rankappagounder Natarajan <jaghu@...gle.com>,
        Patrick Venture <venture@...gle.com>,
        Andrew Jeffery <andrew@...id.au>, devicetree@...r.kernel.org,
        linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] hwmon: (aspeed-pwm-tacho) Deassert reset in probe

On Thu, Nov 02, 2017 at 02:53:48PM +1100, Joel Stanley wrote:
> The ASPEED SoC must deassert a reset in order to use the PWM/tach
> peripheral.
> 
Again, you claim that the current driver would not work at all, which
is simply not correct. It doesn't work if the chip wasn't taken out
of reset by other means. This doesn't take into account situations and
hardware where the chip is taken out of reset automatically at boot,
or by the ROM monitor/BIOS. It assumes that the reset pin can _always_
be controlled by software.

Similar, it forces the chip into reset when the driver is removed,
which is even worse. Unload the driver, and no more fan control ?
Really ? Then why is there an autonomous chip for fan control
to start with ? This is questionable even if the reset pin is
optional.

You'll have to make reset handling optional for me to accept it.
I am quite sure that I said that before.

Guenter

> Signed-off-by: Joel Stanley <joel@....id.au>
> ---
> v2:
>  - Correct horrible mistakes
>  - Boot tested and hwmon sysfs files checked
> ---
>  drivers/hwmon/aspeed-pwm-tacho.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/drivers/hwmon/aspeed-pwm-tacho.c b/drivers/hwmon/aspeed-pwm-tacho.c
> index 63a95e23ca81..77bb7a4bbed4 100644
> --- a/drivers/hwmon/aspeed-pwm-tacho.c
> +++ b/drivers/hwmon/aspeed-pwm-tacho.c
> @@ -19,6 +19,7 @@
>  #include <linux/of_platform.h>
>  #include <linux/platform_device.h>
>  #include <linux/regmap.h>
> +#include <linux/reset.h>
>  #include <linux/sysfs.h>
>  #include <linux/thermal.h>
>  
> @@ -181,6 +182,7 @@ struct aspeed_cooling_device {
>  
>  struct aspeed_pwm_tacho_data {
>  	struct regmap *regmap;
> +	struct reset_control *rst;
>  	unsigned long clk_freq;
>  	bool pwm_present[8];
>  	bool fan_tach_present[16];
> @@ -931,6 +933,15 @@ static int aspeed_pwm_tacho_probe(struct platform_device *pdev)
>  			&aspeed_pwm_tacho_regmap_config);
>  	if (IS_ERR(priv->regmap))
>  		return PTR_ERR(priv->regmap);
> +
> +	priv->rst = devm_reset_control_get_exclusive(dev, NULL);
> +	if (IS_ERR(priv->rst)) {
> +		dev_err(dev,
> +			"missing or invalid reset controller device tree entry");
> +		return PTR_ERR(priv->rst);
> +	}
> +	reset_control_deassert(priv->rst);
> +
>  	regmap_write(priv->regmap, ASPEED_PTCR_TACH_SOURCE, 0);
>  	regmap_write(priv->regmap, ASPEED_PTCR_TACH_SOURCE_EXT, 0);
>  
> @@ -960,6 +971,15 @@ static int aspeed_pwm_tacho_probe(struct platform_device *pdev)
>  	return PTR_ERR_OR_ZERO(hwmon);
>  }
>  
> +static int aspeed_pwm_tacho_remove(struct platform_device *pdev)
> +{
> +	struct aspeed_pwm_tacho_data *priv = platform_get_drvdata(pdev);
> +
> +	reset_control_assert(priv->rst);
> +
> +	return 0;
> +}
> +
>  static const struct of_device_id of_pwm_tacho_match_table[] = {
>  	{ .compatible = "aspeed,ast2400-pwm-tacho", },
>  	{ .compatible = "aspeed,ast2500-pwm-tacho", },
> @@ -969,6 +989,7 @@ MODULE_DEVICE_TABLE(of, of_pwm_tacho_match_table);
>  
>  static struct platform_driver aspeed_pwm_tacho_driver = {
>  	.probe		= aspeed_pwm_tacho_probe,
> +	.remove 	= aspeed_pwm_tacho_remove,
>  	.driver		= {
>  		.name	= "aspeed_pwm_tacho",
>  		.of_match_table = of_pwm_tacho_match_table,
> -- 
> 2.14.1
> 
> --
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