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, 2024-04-23 at 22:22 +0800, Xu Yilun wrote:
> On Tue, Apr 09, 2024 at 11:56:19PM +0000, Colberg, Peter wrote:
> > 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?
> 
> Using devm_*() usually means the lifecycle of the allocated object
> should be the same as the device. Otherwise use the plain allocation.
> Please check which case fits for you.

devm_kzalloc() as used currently is appropriate since the allocated
object should have the same lifetime as the device.

Thanks,
Peter

> 
> Thanks,
> Yilun
> 
> > 
> > [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;
> > >  }
> >