Re: [PATCH v1 07/14] nvmem: core: add per-cell post processing

[Michael Walle]

Hi,

Am 2022-08-30 15:37, schrieb Srinivas Kandagatla:
> On 25/08/2022 22:44, Michael Walle wrote:
> > Instead of relying on the name the consumer is using for the cell, 
> > like
> > it is done for the nvmem .cell_post_process configuration parameter,
> > provide a per-cell post processing hook. This can then be populated by
> > the NVMEM provider (or the NVMEM layout) when adding the cell.
> >
> > Signed-off-by: Michael Walle <michael@xxxxxxxx>
> > ---
> >   drivers/nvmem/core.c           | 16 ++++++++++++++++
> >   include/linux/nvmem-consumer.h |  5 +++++
> >   2 files changed, 21 insertions(+)
> >
> > diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
> > index 5357fc378700..cbfbe6264e6c 100644
> > --- a/drivers/nvmem/core.c
> > +++ b/drivers/nvmem/core.c
> > @@ -52,6 +52,7 @@ struct nvmem_cell_entry {
> >   	int			bytes;
> >   	int			bit_offset;
> >   	int			nbits;
> > +	nvmem_cell_post_process_t post_process;
>
>
> two post_processing callbacks for cells is confusing tbh, we could
> totally move to use of cell->post_process.
>
> one idea is to point cell->post_process to nvmem->cell_post_process
> during cell creation time which should clean this up a bit.

You'll then trigger the read-only check below for all the cells
if nvmem->cell_post_process is set.

> Other option is to move to using layouts for every thing.

As mentioned in a previous reply, I can't see how it could be
achieved. The problem here is that:
 (1) the layout isn't creating the cells, the OF parser is
 (2) even if we would create the cells, we wouldn't know
     which cell needs the post_process. So we are back to
     the situation above, were we have to add it to all
     the cells, making them read-only. [We depend on the
     name of the nvmem-consumer to apply the hook.

> prefixing post_process with read should also make it explicit that
> this callback is very specific to reads only.

good idea.

-michael

> >   	struct device_node	*np;
> >   	struct nvmem_device	*nvmem;
> >   	struct list_head	node;
> > @@ -468,6 +469,7 @@ static int 
> > nvmem_cell_info_to_nvmem_cell_entry_nodup(struct nvmem_device *nvmem,
> >   	cell->offset = info->offset;
> >   	cell->bytes = info->bytes;
> >   	cell->name = info->name;
> > +	cell->post_process = info->post_process;
> >     	cell->bit_offset = info->bit_offset;
> >   	cell->nbits = info->nbits;
> > @@ -1500,6 +1502,13 @@ static int __nvmem_cell_read(struct 
> > nvmem_device *nvmem,
> >   	if (cell->bit_offset || cell->nbits)
> >   		nvmem_shift_read_buffer_in_place(cell, buf);
> >   +	if (cell->post_process) {
> > +		rc = cell->post_process(nvmem->priv, id, index,
> > +					cell->offset, buf, cell->bytes);
> > +		if (rc)
> > +			return rc;
> > +	}
> > +
> >   	if (nvmem->cell_post_process) {
> >   		rc = nvmem->cell_post_process(nvmem->priv, id, index,
> >   					      cell->offset, buf, cell->bytes);
> > @@ -1608,6 +1617,13 @@ static int __nvmem_cell_entry_write(struct 
> > nvmem_cell_entry *cell, void *buf, si
> >   	    (cell->bit_offset == 0 && len != cell->bytes))
> >   		return -EINVAL;
> >   +	/*
> > +	 * Any cells which have a post_process hook are read-only because we
> > +	 * cannot reverse the operation and it might affect other cells, 
> > too.
> > +	 */
> > +	if (cell->post_process)
> > +		return -EINVAL;
>
> Post process was always implicitly for reads only, this check should
> also tie the loose ends of cell_post_processing callback.
>
>
> --srini
> > +
> >   	if (cell->bit_offset || cell->nbits) {
> >   		buf = nvmem_cell_prepare_write_buffer(cell, buf, len);
> >   		if (IS_ERR(buf))
> > diff --git a/include/linux/nvmem-consumer.h 
> > b/include/linux/nvmem-consumer.h
> > index 980f9c9ac0bc..761b8ef78adc 100644
> > --- a/include/linux/nvmem-consumer.h
> > +++ b/include/linux/nvmem-consumer.h
> > @@ -19,6 +19,10 @@ struct device_node;
> >   struct nvmem_cell;
> >   struct nvmem_device;
> >   +/* duplicated from nvmem-provider.h */
> > +typedef int (*nvmem_cell_post_process_t)(void *priv, const char *id, 
> > int index,
> > +					 unsigned int offset, void *buf, size_t bytes);
> > +
> >   struct nvmem_cell_info {
> >   	const char		*name;
> >   	unsigned int		offset;
> > @@ -26,6 +30,7 @@ struct nvmem_cell_info {
> >   	unsigned int		bit_offset;
> >   	unsigned int		nbits;
> >   	struct device_node	*np;
> > +	nvmem_cell_post_process_t post_process;
> >   };
> >     /**