On Fri, Nov 3, 2017 at 1:54 AM, Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> 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, h
> or by the ROM monitor/BIOS. It assumes that the reset pin can _always_
> be controlled by software.
The reset is internal to the SoC. There is no pin to speak of, just a
wire inside the SoC, so it can always be controlled by software.
There's SoC does not release any resets automatically; the default
value on boot is for the reset to be asserted and this is not
configurable.
> 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.
Similarly, the PWM/Tach unit is inside the SoC; it's not an external device.
It would be strange to remove the driver and expect the system to keep
operating normally.
> You'll have to make reset handling optional for me to accept it.
> I am quite sure that I said that before.
Please reconsider in light of the details above. It does not make any
sense to build a system without this reset.
Cheers,
Joel
>
> Guenter
>
>> Signed-off-by: Joel Stanley <joel@xxxxxxxxx>
>> ---
>> 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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