Re: [PATCH 2/3] PWM framework: add support referencing PWMs from ACPI

[Nikolaus Voss <nv@vosn.de>]

Dan,

On Thu, 30 May 2019, Dan Murphy wrote:
> Nikolaus
>
> On 5/29/19 7:18 AM, Nikolaus Voss wrote:
>> In analogy to referencing a GPIO using the "gpios" property from ACPI,
>> support referencing a PWM using the "pwms" property.
>>
>> ACPI entries must look like
>>   Package () {"pwms", Package ()
>>       { <PWM device reference>, <PWM index>, <PWM period> [, <PWM flags>]}}
>>
>> In contrast to the DT implementation, only _one_ PWM entry in the "pwms"
>> property is supported. As a consequence "pwm-names"-property and
>> con_id lookup aren't supported.
>>
>> Support for ACPI is added via the firmware-node framework which is an
>> abstraction layer on top of ACPI/DT. To keep this patch clean, DT and
>> ACPI paths are kept separate. The firmware-node framework could be used
>> to unify both paths in a future patch.
>>
>> To support leds-pwm driver, an additional method devm_fwnode_pwm_get()
>> which supports both ACPI and DT configuration is exported.
>>
>> Signed-off-by: Nikolaus Voss <nikolaus.voss@loewensteinmedical.de>
>> ---
>>   drivers/pwm/core.c  | 112 ++++++++++++++++++++++++++++++++++++++++++++
>>   include/linux/pwm.h |   9 ++++
>>   2 files changed, 121 insertions(+)
>>
>> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
>> index 275b5f399a1a..1d788c05193e 100644
>> --- a/drivers/pwm/core.c
>> +++ b/drivers/pwm/core.c
>> @@ -6,6 +6,7 @@
>>    * Copyright (C) 2011-2012 Avionic Design GmbH
>>    */
>>
>> +#include <linux/acpi.h>
>>   #include <linux/module.h>
>>   #include <linux/pwm.h>
>>   #include <linux/radix-tree.h>
>> @@ -700,6 +701,75 @@ struct pwm_device *of_pwm_get(struct device_node *np, const char *con_id)
>>   }
>>   EXPORT_SYMBOL_GPL(of_pwm_get);
>>
>> +static struct pwm_chip *device_to_pwmchip(struct device *dev)
>> +{
>> +     struct pwm_chip *chip;
>> +
>> +     mutex_lock(&pwm_lock);
>> +
>> +     list_for_each_entry(chip, &pwm_chips, list) {
>> +             struct acpi_device *adev = ACPI_COMPANION(chip->dev);
>> +
>> +             if ((chip->dev == dev) || (adev && &adev->dev == dev)) {
>> +                     mutex_unlock(&pwm_lock);
>> +                     return chip;
>> +             }
>> +     }
>> +
>> +     mutex_unlock(&pwm_lock);
>> +
>> +     return ERR_PTR(-EPROBE_DEFER);
>> +}
>> +
>> +/**
>> + * acpi_pwm_get() - request a PWM via parsing "pwms" property in ACPI
>> + * @fwnode: firmware node to get the "pwm" property from
>> + *
>> + * Returns the PWM device parsed from the fwnode and index specified in the
>> + * "pwms" property or a negative error-code on failure.
>> + * Values parsed from the device tree are stored in the returned PWM device
>> + * object.
>> + *
>> + * This is analogous to of_pwm_get() except con_id is not yet supported.
>> + * ACPI entries must look like
>> + * Package () {"pwms", Package ()
>> + *     { <PWM device reference>, <PWM index>, <PWM period> [, <PWM flags>]}}
>> + *
>> + * Returns: A pointer to the requested PWM device or an ERR_PTR()-encoded
>> + * error code on failure.
>> + */
>> +struct pwm_device *acpi_pwm_get(struct fwnode_handle *fwnode)
> static?
yes, changed.

>> +{
>> +     struct fwnode_reference_args args;
>> +     struct pwm_chip *chip;
>> +     struct pwm_device *pwm = ERR_PTR(-ENODEV);
>> +     int ret;
>> +
>> +     memset(&args, 0, sizeof(args));
>
> args should be zero'd out when initialized on the stack so this is
> necessary.
>
>> +     ret = __acpi_node_get_property_reference(fwnode, "pwms", 0, 3, &args);
>> +
>> +     if (!to_acpi_device_node(args.fwnode))
>> +             return ERR_PTR(-EINVAL);
> Add new line
ok

>> +     if (args.nargs < 2)
>> +             return ERR_PTR(-EPROTO);
>> +
>> +     chip = device_to_pwmchip(&to_acpi_device_node(args.fwnode)->dev);
>> +     if (IS_ERR(chip))
>> +             return ERR_CAST(chip);
>> +
>> +     pwm = pwm_request_from_chip(chip, args.args[0], NULL);
>> +     if (IS_ERR(pwm))
>> +             return pwm;
>> +
>> +     pwm->args.period = args.args[1];
>> +     pwm->args.polarity = PWM_POLARITY_NORMAL;
>> +
>> +     if (args.nargs > 2 && args.args[2] & PWM_POLARITY_INVERTED)
>> +             pwm->args.polarity = PWM_POLARITY_INVERSED;
>> +
>> +     return pwm;
>> +}
>> +
>>   /**
>>    * pwm_add_table() - register PWM device consumers
>>    * @table: array of consumers to register
>> @@ -763,6 +833,10 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
>>       if (IS_ENABLED(CONFIG_OF) && dev && dev->of_node)
>>               return of_pwm_get(dev->of_node, con_id);
>>
>> +     /* then lookup via ACPI */
>> +     if (dev && is_acpi_node(dev->fwnode))
>> +             return acpi_pwm_get(dev->fwnode);
>> +
>>       /*
>>        * We look up the provider in the static table typically provided by
>>        * board setup code. We first try to lookup the consumer device by
>> @@ -942,6 +1016,44 @@ struct pwm_device *devm_of_pwm_get(struct device *dev, struct device_node *np,
>>   }
>>   EXPORT_SYMBOL_GPL(devm_of_pwm_get);
>>
>> +/**
>> + * devm_fwnode_pwm_get() - request a resource managed PWM from firmware node
>> + * @dev: device for PWM consumer
>> + * @fwnode: firmware node to get the PWM from
>> + * @con_id: consumer name
>> + *
>> + * Returns the PWM device parsed from the firmware node. See of_pwm_get() and
>> + * acpi_pwm_get() for a detailed description.
>> + *
>> + * Returns: A pointer to the requested PWM device or an ERR_PTR()-encoded
>> + * error code on failure.
>> + */
>> +struct pwm_device *devm_fwnode_pwm_get(struct device *dev,
>> +                                    struct fwnode_handle *fwnode,
>> +                                    const char *con_id)
>
> I am wondering if it would be better just to convert the existing of_
> calls to device_property calls and make it more generic.

With this first patch I wanted to keep DT and ACPI paths separate. Merging 
the two paths as far as possible is reasonable but should be done in a 
second step.

Nikolaus