Re: [PATCH v4 3/5] nvmem: core: Add consumer API to get nvmem cell from node

Srinivas Kandagatla
2016-07-08T17:24:06Z

On 08/07/16 17:42, Stefan Agner wrote:
> On 2016-07-08 08:41, Srinivas Kandagatla wrote:
>> On 07/07/16 14:48, maitysanchayan@gmail.com wrote:
>>> Hello Srinivas,
>>>
>>> On 16-07-07 1

...

>>>>>
>>>>> Our requirement is to be able to pass the soc node pointer and then
>>>>> be able to get a nvmem cell by specifying it's name. So for our case
>>>>
>>>> Why?
>>>
>>> Sorry for not providing the background directly. The patches before this
>>> series used that approach. In the previous discussions it has been pointed
>>> out that it is not acceptable to have additional device tree bindings for
>>> providing data that the driver wants at the SoC node level or to have bindings
>>> just for the SoC bus driver alone since we aren't really describing the
>>> hardware.
>>>
>> SOC driver seems to search for an arbitrary node by its name, which is
>> not a binding and can break anytime in cases If the scope of nvmem
>> provider is out of soc node or if the nvmem cells are not named as
>> expected. That looks very fragile.
>
> In that case, that just "won't happen" because the soc driver is a very
> soc specific driver only used for this device tree. We it will always
> bind to that high level soc node.
>
>>
>> If the soc node is actual consumer of nvmem cells, I see no reason why
>> we should not use proper nvmem bindings?
>
> There is a reason: We don't describe the hardware with it...
>
> The cfg0/cfg1 register which Sanchayan needs to read in the soc bus
> driver are just two register with a unique ID of the SoC. In whatever

"Unique ID of the SOC" doesn't this mean that its a part of soc hw
description/configuration/setup?

Am still not clear why this setup any different to other use cases like
mac address/calibration data?

I still feel that this should be described in the DT.

Rob,
What do you think?

> driver throughout the system we use that ID (e.g. in a random generator
> for initialization) we never describe an actual hardware relation... Its
> just software and how we use that unique ID. The device tree is ment to
> describe hardware. Hence the NVMEM consumer binding is not suited for
> such NVMEM cells...
>
> By describing the NVMEM cells location in device tree (producer API, the
> NVMEM cells are in hardware at that location, so using the device tree
> for that part is fine) and hard coding the NVMEM cell we need in the
> driver code we don't violate the device tree matra "describe the
> hardware"...

IMHO, We should indeed describe the SOC hardware and its relationship
w.r.t to nvmem provider in device tree. Reasoning being these both are
some form of IP blocks/hw which depend on each other.

>
> Looking-up the nodes direcly is what Rob suggested here:
> https://lkml.org/lkml/2016/5/23/573

I did read this, I was not convinced that we should do a direct lookup
for nvmem cells.

thanks,
srini
>
>>
>> Given the fact that the patch is potentially bypassing the nvmem
>> bindings, am not happy to take it!
>
> If you can provide a solution acceptable by the device tree folks and
> works without this patch, I am happy to do it...

>
> Btw, I am not entirely happy with the API name, but did not had a better
> idea... And we we should probably add a note that the device tree
> consumer binding is the preferred way to do it.
>
> --
> Stefan
>
>
>>
>> thanks,
>> srini
>>
>>> For the discussion,
>>> https://lkml.org/lkml/2016/5/23/573
>>> https://lkml.org/lkml/2016/5/2/71
>>>
>>> Regards,
>>> Sanchayan.
>>>
>>>
>>>>
>>>>> ocotp node has cfg0 and cfg1 which we want but we cannot use existing
>>>>> nvmem consumer API since that requires having the nvmem consumer properties
>>>>> in the node we are binding to viz. is a direct nvmem consumer.
>>>>>
>>>>> Regards,
>>>>> Sanchayan.
>>>>>
>>>>>>
>>>>>> thanks,
>>>>>> srini
>>>>>>>
>>>>>>> Parent node can also be the of_node of the main SoC device
>>>>>>> node.
>>>>>>>
>>>>>>> Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>
>>>>>>> ---
>>>>>>> drivers/nvmem/core.c | 44 +++++++++++++++++++++++++++++-------------
>>>>>>> include/linux/nvmem-consumer.h | 1 +
>>>>>>> 2 files changed, 32 insertions(+), 13 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c
>>>>>>> index 965911d..470abee 100644
>>>>>>> --- a/drivers/nvmem/core.c
>>>>>>> +++ b/drivers/nvmem/core.c
>>>>>>> @@ -743,29 +743,21 @@ static struct nvmem_cell *nvmem_cell_get_from_list(const char *cell_id)
>>>>>>>
>>>>>>> #if IS_ENABLED(CONFIG_NVMEM) && IS_ENABLED(CONFIG_OF)
>>>>>>> /**
>>>>>>> - * of_nvmem_cell_get() - Get a nvmem cell from given device node and cell id
>>>>>>> + * of_nvmem_cell_get_direct() - Get a nvmem cell from given device node
>>>>>>> *
>>>>>>> - * @dev node: Device tree node that uses the nvmem cell
>>>>>>> - * @id: nvmem cell name from nvmem-cell-names property.
>>>>>>> + * @dev node: Device tree node that uses nvmem cell
>>>>>>> *
>>>>>>> * Return: Will be an ERR_PTR() on error or a valid pointer
>>>>>>> * to a struct nvmem_cell. The nvmem_cell will be freed by the
>>>>>>> * nvmem_cell_put().
>>>>>>> */
>>>>>>> -struct nvmem_cell *of_nvmem_cell_get(struct device_node *np,
>>>>>>> - const char *name)
>>>>>>> +struct nvmem_cell *of_nvmem_cell_get_direct(struct device_node *cell_np)
>>>>>>> {
>>>>>>> - struct device_node *cell_np, *nvmem_np;
>>>>>>> + struct device_node *nvmem_np;
>>>>>>> struct nvmem_cell *cell;
>>>>>>> struct nvmem_device *nvmem;
>>>>>>> const __be32 *addr;
>>>>>>> - int rval, len, index;
>>>>>>> -
>>>>>>> - index = of_property_match_string(np, "nvmem-cell-names", name);
>>>>>>> -
>>>>>>> - cell_np = of_parse_phandle(np, "nvmem-cells", index);
>>>>>>> - if (!cell_np)
>>>>>>> - return ERR_PTR(-EINVAL);
>>>>>>> + int rval, len;
>>>>>>>
>>>>>>> nvmem_np = of_get_next_parent(cell_np);
>>>>>>> if (!nvmem_np)
>>>>>>> @@ -824,6 +816,32 @@ err_mem:
>>>>>>>
>>>>>>> return ERR_PTR(rval);
>>>>>>> }
>>>>>>> +EXPORT_SYMBOL_GPL(of_nvmem_cell_get_direct);
>>>>>>> +
>>>>>>> +/**
>>>>>>> + * of_nvmem_cell_get() - Get a nvmem cell from given device node and cell id
>>>>>>> + *
>>>>>>> + * @dev node: Device tree node that uses the nvmem cell
>>>>>>> + * @id: nvmem cell name from nvmem-cell-names property.
>>>>>>> + *
>>>>>>> + * Return: Will be an ERR_PTR() on error or a valid pointer
>>>>>>> + * to a struct nvmem_cell. The nvmem_cell will be freed by the
>>>>>>> + * nvmem_cell_put().
>>>>>>> + */
>>>>>>> +struct nvmem_cell *of_nvmem_cell_get(struct device_node *np,
>>>>>>> + const char *name)
>>>>>>> +{
>>>>>>> + struct device_node *cell_np;
>>>>>>> + int index;
>>>>>>> +
>>>>>>> + index = of_property_match_string(np, "nvmem-cell-names", name);
>>>>>>> +
>>>>>>> + cell_np = of_parse_phandle(np, "nvmem-cells", index);
>>>>>>> + if (!cell_np)
>>>>>>> + return ERR_PTR(-EINVAL);
>>>>>>> +
>>>>>>> + return of_nvmem_cell_get_direct(cell_np);
>>>>>>> +}
>>>>>>> EXPORT_SYMBOL_GPL(of_nvmem_cell_get);
>>>>>>> #endif
>>>>>>>
>>>>>>> diff --git a/include/linux/nvmem-consumer.h b/include/linux/nvmem-consumer.h
>>>>>>> index 9bb77d3..bf879fc 100644
>>>>>>> --- a/include/linux/nvmem-consumer.h
>>>>>>> +++ b/include/linux/nvmem-consumer.h
>>>>>>> @@ -136,6 +136,7 @@ static inline int nvmem_device_write(struct nvmem_device *nvmem,
>>>>>>> #endif /* CONFIG_NVMEM */
>>>>>>>
>>>>>>> #if IS_ENABLED(CONFIG_NVMEM) && IS_ENABLED(CONFIG_OF)
>>>>>>> +struct nvmem_cell *of_nvmem_cell_get_direct(struct device_node *cell_np);
>>>>>>> struct nvmem_cell *of_nvmem_cell_get(struct device_node *np,
>>>>>>> const char *name);
>>>>>>> struct nvmem_device *of_nvmem_device_get(struct device_node *np,
>>>>>>>