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Date:   Sun, 24 May 2020 14:09:19 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Alexandru Ardelean <alexandru.ardelean@...log.com>
Cc:     <linux-iio@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <mcoquelin.stm32@...il.com>,
        <alexandre.torgue@...com>
Subject: Re: [PATCH] iio: stm32-adc: keep a reference to the iio device on
 the state struct

On Fri, 22 May 2020 16:07:19 +0300
Alexandru Ardelean <alexandru.ardelean@...log.com> wrote:

> We may want to get rid of the iio_priv_to_dev() helper. The reason is that
> we will hide some of the members of the iio_dev structure (to prevent
> drivers from accessing them directly), and that will also mean hiding the
> implementation of the iio_priv_to_dev() helper inside the IIO core.
> 
> Hiding the implementation of iio_priv_to_dev() implies that some fast-paths
> may not be fast anymore, so a general idea is to try to get rid of the
> iio_priv_to_dev() altogether.
> The iio_priv() helper won't be affected by the rework.
> 
> For this driver, not using iio_priv_to_dev(), means keeping a reference to
> the IIO device on the state struct.
> 
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@...log.com>

I don't particularly mind this approach, but an alternative would be to
change the callbacks to take an iio_dev rather than the iio_priv()
structure.  It's more invasive though as need to change what is
provided via dev_get_drvdata for the adc device.
It's possible I missed a path where this won't work for some reason though.

Up to the driver maintainers on which one they prefer.

Thanks,

Jonathan


> ---
>  drivers/iio/adc/stm32-adc.c | 27 +++++++++++++++------------
>  1 file changed, 15 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/iio/adc/stm32-adc.c b/drivers/iio/adc/stm32-adc.c
> index ae622ee6d08c..7e58c4443e3f 100644
> --- a/drivers/iio/adc/stm32-adc.c
> +++ b/drivers/iio/adc/stm32-adc.c
> @@ -171,6 +171,7 @@ struct stm32_adc_cfg {
>  
>  /**
>   * struct stm32_adc - private data of each ADC IIO instance
> + * @indio_dev:		back-reference to the IIO device object
>   * @common:		reference to ADC block common data
>   * @offset:		ADC instance register offset in ADC block
>   * @cfg:		compatible configuration data
> @@ -194,6 +195,7 @@ struct stm32_adc_cfg {
>   * @chan_name:		channel name array
>   */
>  struct stm32_adc {
> +	struct iio_dev		*indio_dev;
>  	struct stm32_adc_common	*common;
>  	u32			offset;
>  	const struct stm32_adc_cfg	*cfg;
> @@ -637,7 +639,7 @@ static void stm32h7_adc_start_conv(struct stm32_adc *adc, bool dma)
>  
>  static void stm32h7_adc_stop_conv(struct stm32_adc *adc)
>  {
> -	struct iio_dev *indio_dev = iio_priv_to_dev(adc);
> +	struct iio_dev *indio_dev = adc->indio_dev;
>  	int ret;
>  	u32 val;
>  
> @@ -654,7 +656,7 @@ static void stm32h7_adc_stop_conv(struct stm32_adc *adc)
>  
>  static int stm32h7_adc_exit_pwr_down(struct stm32_adc *adc)
>  {
> -	struct iio_dev *indio_dev = iio_priv_to_dev(adc);
> +	struct iio_dev *indio_dev = adc->indio_dev;
>  	int ret;
>  	u32 val;
>  
> @@ -692,7 +694,7 @@ static void stm32h7_adc_enter_pwr_down(struct stm32_adc *adc)
>  
>  static int stm32h7_adc_enable(struct stm32_adc *adc)
>  {
> -	struct iio_dev *indio_dev = iio_priv_to_dev(adc);
> +	struct iio_dev *indio_dev = adc->indio_dev;
>  	int ret;
>  	u32 val;
>  
> @@ -715,7 +717,7 @@ static int stm32h7_adc_enable(struct stm32_adc *adc)
>  
>  static void stm32h7_adc_disable(struct stm32_adc *adc)
>  {
> -	struct iio_dev *indio_dev = iio_priv_to_dev(adc);
> +	struct iio_dev *indio_dev = adc->indio_dev;
>  	int ret;
>  	u32 val;
>  
> @@ -735,7 +737,7 @@ static void stm32h7_adc_disable(struct stm32_adc *adc)
>   */
>  static int stm32h7_adc_read_selfcalib(struct stm32_adc *adc)
>  {
> -	struct iio_dev *indio_dev = iio_priv_to_dev(adc);
> +	struct iio_dev *indio_dev = adc->indio_dev;
>  	int i, ret;
>  	u32 lincalrdyw_mask, val;
>  
> @@ -779,7 +781,7 @@ static int stm32h7_adc_read_selfcalib(struct stm32_adc *adc)
>   */
>  static int stm32h7_adc_restore_selfcalib(struct stm32_adc *adc)
>  {
> -	struct iio_dev *indio_dev = iio_priv_to_dev(adc);
> +	struct iio_dev *indio_dev = adc->indio_dev;
>  	int i, ret;
>  	u32 lincalrdyw_mask, val;
>  
> @@ -852,7 +854,7 @@ static int stm32h7_adc_restore_selfcalib(struct stm32_adc *adc)
>   */
>  static int stm32h7_adc_selfcalib(struct stm32_adc *adc)
>  {
> -	struct iio_dev *indio_dev = iio_priv_to_dev(adc);
> +	struct iio_dev *indio_dev = adc->indio_dev;
>  	int ret;
>  	u32 val;
>  
> @@ -1228,7 +1230,7 @@ static int stm32_adc_read_raw(struct iio_dev *indio_dev,
>  static irqreturn_t stm32_adc_threaded_isr(int irq, void *data)
>  {
>  	struct stm32_adc *adc = data;
> -	struct iio_dev *indio_dev = iio_priv_to_dev(adc);
> +	struct iio_dev *indio_dev = adc->indio_dev;
>  	const struct stm32_adc_regspec *regs = adc->cfg->regs;
>  	u32 status = stm32_adc_readl(adc, regs->isr_eoc.reg);
>  
> @@ -1241,7 +1243,7 @@ static irqreturn_t stm32_adc_threaded_isr(int irq, void *data)
>  static irqreturn_t stm32_adc_isr(int irq, void *data)
>  {
>  	struct stm32_adc *adc = data;
> -	struct iio_dev *indio_dev = iio_priv_to_dev(adc);
> +	struct iio_dev *indio_dev = adc->indio_dev;
>  	const struct stm32_adc_regspec *regs = adc->cfg->regs;
>  	u32 status = stm32_adc_readl(adc, regs->isr_eoc.reg);
>  
> @@ -1879,6 +1881,7 @@ static int stm32_adc_probe(struct platform_device *pdev)
>  		return -ENOMEM;
>  
>  	adc = iio_priv(indio_dev);
> +	adc->indio_dev = indio_dev;
>  	adc->common = dev_get_drvdata(pdev->dev.parent);
>  	spin_lock_init(&adc->lock);
>  	init_completion(&adc->completion);
> @@ -1990,7 +1993,7 @@ static int stm32_adc_probe(struct platform_device *pdev)
>  static int stm32_adc_remove(struct platform_device *pdev)
>  {
>  	struct stm32_adc *adc = platform_get_drvdata(pdev);
> -	struct iio_dev *indio_dev = iio_priv_to_dev(adc);
> +	struct iio_dev *indio_dev = adc->indio_dev;
>  
>  	pm_runtime_get_sync(&pdev->dev);
>  	iio_device_unregister(indio_dev);
> @@ -2013,7 +2016,7 @@ static int stm32_adc_remove(struct platform_device *pdev)
>  static int stm32_adc_suspend(struct device *dev)
>  {
>  	struct stm32_adc *adc = dev_get_drvdata(dev);
> -	struct iio_dev *indio_dev = iio_priv_to_dev(adc);
> +	struct iio_dev *indio_dev = adc->indio_dev;
>  
>  	if (iio_buffer_enabled(indio_dev))
>  		__stm32_adc_buffer_predisable(indio_dev);
> @@ -2024,7 +2027,7 @@ static int stm32_adc_suspend(struct device *dev)
>  static int stm32_adc_resume(struct device *dev)
>  {
>  	struct stm32_adc *adc = dev_get_drvdata(dev);
> -	struct iio_dev *indio_dev = iio_priv_to_dev(adc);
> +	struct iio_dev *indio_dev = adc->indio_dev;
>  	int ret;
>  
>  	ret = pm_runtime_force_resume(dev);

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