Re: [RFC PATCH v2 3/9] fpga: dfl: migrate AFU MMIO region management driver to dfl_feature_dev_data

["Colberg, Peter" <peter.colberg@intel.com>]

On Tue, 2024-04-09 at 19:39 -0400, Peter Colberg wrote:
> This change separates out most of the symbol name changes required by this
> patch series for the file: drivers/fpga/dfl-afu-region.c. This is done to
> split a single monolithic change into multiple, smaller patches at the
> request of the maintainer.
> 
> Signed-off-by: Peter Colberg <peter.colberg@intel.com>
> ---
> v2:
> - Split monolithic patch into series at request of maintainer
> ---
>  drivers/fpga/dfl-afu-region.c | 51 ++++++++++++++++++-----------------
>  1 file changed, 26 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/fpga/dfl-afu-region.c b/drivers/fpga/dfl-afu-region.c
> index 2e7b41629406..b11a5b21e666 100644
> --- a/drivers/fpga/dfl-afu-region.c
> +++ b/drivers/fpga/dfl-afu-region.c
> @@ -12,11 +12,11 @@
>  
>  /**
>   * afu_mmio_region_init - init function for afu mmio region support
> - * @pdata: afu platform device's pdata.
> + * @fdata: afu feature dev data
>   */
> -void afu_mmio_region_init(struct dfl_feature_platform_data *pdata)
> +void afu_mmio_region_init(struct dfl_feature_dev_data *fdata)
>  {
> -	struct dfl_afu *afu = dfl_fpga_pdata_get_private(pdata);
> +	struct dfl_afu *afu = dfl_fpga_fdata_get_private(fdata);
>  
>  	INIT_LIST_HEAD(&afu->regions);
>  }
> @@ -39,7 +39,7 @@ static struct dfl_afu_mmio_region *get_region_by_index(struct dfl_afu *afu,
>  /**
>   * afu_mmio_region_add - add a mmio region to given feature dev.
>   *
> - * @pdata: afu platform device's pdata.
> + * @fdata: afu feature dev data
>   * @region_index: region index.
>   * @region_size: region size.
>   * @phys: region's physical address of this region.
> @@ -47,14 +47,15 @@ static struct dfl_afu_mmio_region *get_region_by_index(struct dfl_afu *afu,
>   *
>   * Return: 0 on success, negative error code otherwise.
>   */
> -int afu_mmio_region_add(struct dfl_feature_platform_data *pdata,
> +int afu_mmio_region_add(struct dfl_feature_dev_data *fdata,
>  			u32 region_index, u64 region_size, u64 phys, u32 flags)
>  {
> +	struct device *dev = &fdata->dev->dev;
>  	struct dfl_afu_mmio_region *region;
>  	struct dfl_afu *afu;
>  	int ret = 0;
>  
> -	region = devm_kzalloc(&pdata->dev->dev, sizeof(*region), GFP_KERNEL);
> +	region = devm_kzalloc(dev, sizeof(*region), GFP_KERNEL);
>  	if (!region)
>  		return -ENOMEM;
>  
> @@ -63,13 +64,13 @@ int afu_mmio_region_add(struct dfl_feature_platform_data *pdata,
>  	region->phys = phys;
>  	region->flags = flags;
>  
> -	mutex_lock(&pdata->lock);
> +	mutex_lock(&fdata->lock);
>  
> -	afu = dfl_fpga_pdata_get_private(pdata);
> +	afu = dfl_fpga_fdata_get_private(fdata);
>  
>  	/* check if @index already exists */
>  	if (get_region_by_index(afu, region_index)) {
> -		mutex_unlock(&pdata->lock);
> +		mutex_unlock(&fdata->lock);
>  		ret = -EEXIST;
>  		goto exit;
>  	}
> @@ -80,37 +81,37 @@ int afu_mmio_region_add(struct dfl_feature_platform_data *pdata,
>  
>  	afu->region_cur_offset += region_size;
>  	afu->num_regions++;
> -	mutex_unlock(&pdata->lock);
> +	mutex_unlock(&fdata->lock);
>  
>  	return 0;
>  
>  exit:
> -	devm_kfree(&pdata->dev->dev, region);
> +	devm_kfree(dev, region);

An internal reviewer commented that calling devm_kfree() in almost all
cases shows a misunderstanding of object lifetime and may unveil bugs.
They suggested to either drop the explicit devm_kfree(), or move from
devm_*() to plain allocation.

I could not find specific documentation on the recommended use cases
for devm_kfree() to immediately free a resource on error, but the
description of devres groups advises that explicit freeing using
devres_release_group() is usually useful in midlayer drivers where
interface functions should not have side effects [1].

Which implementation would you prefer and why? Dropping devm_kfree(),
moving to plain allocation, or leaving everything as is?

[1] https://docs.kernel.org/driver-api/driver-model/devres.html#devres-group 

Thanks,
Peter

>  	return ret;
>  }
>  
>  /**
>   * afu_mmio_region_destroy - destroy all mmio regions under given feature dev.
> - * @pdata: afu platform device's pdata.
> + * @fdata: afu feature dev data
>   */
> -void afu_mmio_region_destroy(struct dfl_feature_platform_data *pdata)
> +void afu_mmio_region_destroy(struct dfl_feature_dev_data *fdata)
>  {
> -	struct dfl_afu *afu = dfl_fpga_pdata_get_private(pdata);
> +	struct dfl_afu *afu = dfl_fpga_fdata_get_private(fdata);
>  	struct dfl_afu_mmio_region *tmp, *region;
>  
>  	list_for_each_entry_safe(region, tmp, &afu->regions, node)
> -		devm_kfree(&pdata->dev->dev, region);
> +		devm_kfree(&fdata->dev->dev, region);
>  }
>  
>  /**
>   * afu_mmio_region_get_by_index - find an afu region by index.
> - * @pdata: afu platform device's pdata.
> + * @fdata: afu feature dev data
>   * @region_index: region index.
>   * @pregion: ptr to region for result.
>   *
>   * Return: 0 on success, negative error code otherwise.
>   */
> -int afu_mmio_region_get_by_index(struct dfl_feature_platform_data *pdata,
> +int afu_mmio_region_get_by_index(struct dfl_feature_dev_data *fdata,
>  				 u32 region_index,
>  				 struct dfl_afu_mmio_region *pregion)
>  {
> @@ -118,8 +119,8 @@ int afu_mmio_region_get_by_index(struct dfl_feature_platform_data *pdata,
>  	struct dfl_afu *afu;
>  	int ret = 0;
>  
> -	mutex_lock(&pdata->lock);
> -	afu = dfl_fpga_pdata_get_private(pdata);
> +	mutex_lock(&fdata->lock);
> +	afu = dfl_fpga_fdata_get_private(fdata);
>  	region = get_region_by_index(afu, region_index);
>  	if (!region) {
>  		ret = -EINVAL;
> @@ -127,14 +128,14 @@ int afu_mmio_region_get_by_index(struct dfl_feature_platform_data *pdata,
>  	}
>  	*pregion = *region;
>  exit:
> -	mutex_unlock(&pdata->lock);
> +	mutex_unlock(&fdata->lock);
>  	return ret;
>  }
>  
>  /**
>   * afu_mmio_region_get_by_offset - find an afu mmio region by offset and size
>   *
> - * @pdata: afu platform device's pdata.
> + * @fdata: afu feature dev data
>   * @offset: region offset from start of the device fd.
>   * @size: region size.
>   * @pregion: ptr to region for result.
> @@ -144,7 +145,7 @@ int afu_mmio_region_get_by_index(struct dfl_feature_platform_data *pdata,
>   *
>   * Return: 0 on success, negative error code otherwise.
>   */
> -int afu_mmio_region_get_by_offset(struct dfl_feature_platform_data *pdata,
> +int afu_mmio_region_get_by_offset(struct dfl_feature_dev_data *fdata,
>  				  u64 offset, u64 size,
>  				  struct dfl_afu_mmio_region *pregion)
>  {
> @@ -152,8 +153,8 @@ int afu_mmio_region_get_by_offset(struct dfl_feature_platform_data *pdata,
>  	struct dfl_afu *afu;
>  	int ret = 0;
>  
> -	mutex_lock(&pdata->lock);
> -	afu = dfl_fpga_pdata_get_private(pdata);
> +	mutex_lock(&fdata->lock);
> +	afu = dfl_fpga_fdata_get_private(fdata);
>  	for_each_region(region, afu)
>  		if (region->offset <= offset &&
>  		    region->offset + region->size >= offset + size) {
> @@ -162,6 +163,6 @@ int afu_mmio_region_get_by_offset(struct dfl_feature_platform_data *pdata,
>  		}
>  	ret = -EINVAL;
>  exit:
> -	mutex_unlock(&pdata->lock);
> +	mutex_unlock(&fdata->lock);
>  	return ret;
>  }