Date:   Wed, 10 Mar 2021 09:55:45 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Andreas Kemnade <andreas@...nade.info>
Cc:     j.neuschaefer@....net, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mfd: ntxec: Support for EC in Tolino Shine 2 HD

On Mon, 08 Mar 2021, Andreas Kemnade wrote:

> Add the version of the EC in the Tolino Shine 2 HD
> to the supported versions. It seems not to have an RTC
> and does not ack data written to it.
> The vendor kernel happily ignores write errors, using
> I2C via userspace i2c-set also shows the error.
> So add a quirk to ignore that error.
> 
> PWM can be successfully configured despite of that error.
> 
> Signed-off-by: Andreas Kemnade <andreas@...nade.info>
> ---
> Changes in v2:
> - more comments about stacking regmap construction
> - fix accidential line removal
> - better naming for subdevices
> 
>  drivers/mfd/ntxec.c       | 61 +++++++++++++++++++++++++++++++++++++--
>  include/linux/mfd/ntxec.h |  1 +
>  2 files changed, 59 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/mfd/ntxec.c b/drivers/mfd/ntxec.c
> index 957de2b03529..0bbd2e34e89c 100644
> --- a/drivers/mfd/ntxec.c
> +++ b/drivers/mfd/ntxec.c
> @@ -96,6 +96,38 @@ static struct notifier_block ntxec_restart_handler = {
>  	.priority = 128,
>  };
>  
> +static int regmap_ignore_write(void *context,
> +			       unsigned int reg, unsigned int val)
> +
> +{
> +	struct regmap *regmap = context;
> +
> +	regmap_write(regmap, reg, val);
> +
> +	return 0;
> +}
> +
> +static int regmap_wrap_read(void *context, unsigned int reg,
> +			    unsigned int *val)
> +{
> +	struct regmap *regmap = context;
> +
> +	return regmap_read(regmap, reg, val);
> +}
> +
> +/*
> + * Some firmware versions do not ack written data, add a wrapper. It
> + * is used to stack another regmap on top.
> + */
> +static const struct regmap_config regmap_config_noack = {
> +	.name = "ntxec_noack",
> +	.reg_bits = 8,
> +	.val_bits = 16,
> +	.cache_type = REGCACHE_NONE,
> +	.reg_write = regmap_ignore_write,
> +	.reg_read = regmap_wrap_read
> +};
> +
>  static const struct regmap_config regmap_config = {
>  	.name = "ntxec",
>  	.reg_bits = 8,
> @@ -104,15 +136,20 @@ static const struct regmap_config regmap_config = {
>  	.val_format_endian = REGMAP_ENDIAN_BIG,
>  };
>  
> -static const struct mfd_cell ntxec_subdevices[] = {
> +static const struct mfd_cell ntxec_subdev[] = {
>  	{ .name = "ntxec-rtc" },
>  	{ .name = "ntxec-pwm" },
>  };
>  
> +static const struct mfd_cell ntxec_subdev_pwm[] = {
> +	{ .name = "ntxec-pwm" },
> +};

To put across what you're trying to achieve, maybe call this:

  ntxec_subdev_no_rtc[]

Then if other devices are added, the semantics/intent stays the same
and it won't have to be renamed.

>  static int ntxec_probe(struct i2c_client *client)
>  {
>  	struct ntxec *ec;
>  	unsigned int version;
> +	bool has_rtc;
>  	int res;
>  
>  	ec = devm_kmalloc(&client->dev, sizeof(*ec), GFP_KERNEL);
> @@ -137,6 +174,16 @@ static int ntxec_probe(struct i2c_client *client)
>  	/* Bail out if we encounter an unknown firmware version */
>  	switch (version) {
>  	case NTXEC_VERSION_KOBO_AURA:
> +		has_rtc = true;
> +		break;
> +	case NTXEC_VERSION_TOLINO_SHINE2:
> +		has_rtc = false;
> +		/* Another regmap stacked on top of the other */
> +		ec->regmap = devm_regmap_init(ec->dev, NULL,
> +					      ec->regmap,
> +					      &regmap_config_noack);
> +		if (IS_ERR(ec->regmap))
> +			return PTR_ERR(ec->regmap);
>  		break;
>  	default:
>  		dev_err(ec->dev,
> @@ -181,8 +228,16 @@ static int ntxec_probe(struct i2c_client *client)
>  
>  	i2c_set_clientdata(client, ec);
>  
> -	res = devm_mfd_add_devices(ec->dev, PLATFORM_DEVID_NONE, ntxec_subdevices,
> -				   ARRAY_SIZE(ntxec_subdevices), NULL, 0, NULL);
> +	if (has_rtc)
> +		res = devm_mfd_add_devices(ec->dev, PLATFORM_DEVID_NONE,
> +					   ntxec_subdev,
> +					   ARRAY_SIZE(ntxec_subdev),
> +					   NULL, 0, NULL);
> +	else
> +		res = devm_mfd_add_devices(ec->dev, PLATFORM_DEVID_NONE,
> +					   ntxec_subdev_pwm,
> +					   ARRAY_SIZE(ntxec_subdev_pwm),
> +					   NULL, 0, NULL);

You're over-complicating things.

Simply have a local mfd_cells variable that you assign either
'ntxec_subdev' or 'ntxec_subdev_pwm' to, then simply call
devm_mfd_add_devices() once.

It means you can also drop 'has_rtc'.

>  	if (res)
>  		dev_err(ec->dev, "Failed to add subdevices: %d\n", res);
>  
> diff --git a/include/linux/mfd/ntxec.h b/include/linux/mfd/ntxec.h
> index 361204d125f1..26ab3b8eb612 100644
> --- a/include/linux/mfd/ntxec.h
> +++ b/include/linux/mfd/ntxec.h
> @@ -33,5 +33,6 @@ static inline __be16 ntxec_reg8(u8 value)
>  
>  /* Known firmware versions */
>  #define NTXEC_VERSION_KOBO_AURA	0xd726	/* found in Kobo Aura */
> +#define NTXEC_VERSION_TOLINO_SHINE2 0xf110 /* found in Tolino Shine 2 HD */
>  
>  #endif

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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