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

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Message-ID: <1331f460-d34b-02b2-d41a-3d0ec9543bb5@roeck-us.net>
Date:   Tue, 31 Oct 2017 19:14:37 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Stafford Horne <shorne@...il.com>
Cc:     Joel Stanley <joel@....id.au>, Rob Herring <robh+dt@...nel.org>,
        Philipp Zabel <philipp.zabel@...il.com>,
        Mykola Kostenok <c_mykolak@...lanox.com>,
        Jaghathiswari Rankappagounder Natarajan <jaghu@...gle.com>,
        devicetree@...r.kernel.org, linux-hwmon@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: (aspeed-pwm-tacho) Deassert reset in probe

On 10/31/2017 07:04 PM, Stafford Horne wrote:
> On Tue, Oct 31, 2017 at 06:53:15PM -0700, Guenter Roeck wrote:
>> On 10/31/2017 06:34 PM, Joel Stanley wrote:
>>> The ASPEED SoC must deassert a reset in order to use the PWM/tach
>>> peripheral.
>>>
>>> The device tree bindings are updated to document the resets phandle, and
>>> the example is updated to match what is expected for both the reset and
>>> clock phandle. Note that the bindings should have always had the reset
>>> controller, as the hardware is unusable without it.
>>>
>>> Signed-off-by: Joel Stanley <joel@....id.au>
>>
>> Presumably the driver is being used. This change makes it incompatible with
>> existing users. This is unacceptable; after all, it is possible that the
>> device is taken out of reset by ROMMON or BIOS.
>>
>> On top of that, the reset controller code is quite strict and issues a
>> backtrace if CONFIG_RESET_CONTROLLER is not enabled. Yet, there is no
>> dependency added on RESET_CONTROLLER. You might want to consider making
>> the new control optional and using devm_reset_control_get_optional_exclusive().
>>
>> The DT change should be a separate patch.
>>
>> More comments below.
> 
> [..]
> 
>>>    	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_deassert(priv->rst);
>>
>> This seems to be quite pointless. Also, did you test this code ?
>>
>>> +
>>> +	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,
>>> +	.probe		= aspeed_pwm_tacho_remove,
> 
> Also, this cant be right (should be .remove)?
> 

Nice. Makes me really wonder what this code would do. Does this even compile ?

Guenter