On Tue, 28 Aug 2018 16:41:04 +0200 Bartosz Golaszewski <brgl@xxxxxxxx> wrote: > 2018-08-28 15:45 GMT+02:00 Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>: > > > > > > On 28/08/18 12:56, Bartosz Golaszewski wrote: > >> > >> 2018-08-28 12:15 GMT+02:00 Srinivas Kandagatla > >> <srinivas.kandagatla@xxxxxxxxxx>: > >>> > >>> > >>> On 27/08/18 14:37, Bartosz Golaszewski wrote: > >>>> > >>>> > >>>> I didn't notice it before but there's a global list of nvmem cells > >>> > >>> > >>> > >>> Bit of history here. > >>> > >>> The global list of nvmem_cell is to assist non device tree based cell > >>> lookups. These cell entries come as part of the non-dt providers > >>> nvmem_config. > >>> > >>> All the device tree based cell lookup happen dynamically on > >>> request/demand, > >>> and all the cell definition comes from DT. > >>> > >> > >> Makes perfect sense. > >> > >>> As of today NVMEM supports both DT and non DT usecase, this is much > >>> simpler. > >>> > >>> Non dt cases have various consumer usecases. > >>> > >>> 1> Consumer is aware of provider name and cell details. > >>> This is probably simple usecase where it can just use device > >>> based > >>> apis. > >>> > >>> 2> Consumer is not aware of provider name, its just aware of cell name. > >>> This is the case where global list of cells are used. > >>> > >> > >> I would like to support an additional use case here: the provider is > >> generic and is not aware of its cells at all. Since the only way of > >> defining nvmem cells is through DT or nvmem_config, we lack a way to > >> allow machine code to define cells without the provider code being > >> aware. > > > > > > machine driver should be able to do > > nvmem_device_get() > > nvmem_add_cells() > > > > Indeed, I missed the fact that you can retrieve the nvmem device by > name. Except that we cannot know that the nvmem provider has been > registered yet when calling nvmem_device_get(). This could potentially > be solved by my other patch that adds notifiers to nvmem, but it would > require much more boilerplate code in every board file. I think that > removing nvmem_cell_info from nvmem_config and having external cell > definitions would be cleaner. I also vote for this option. > > > > static struct nvmem_cell *nvmem_find_cell(const char *cell_id) Can we get rid of this function and just have the the version that takes an nvmem_name and a cell_id. > >> Yes, I would like to rework nvmem a bit. I don't see any non-DT users > >> defining nvmem-cells using nvmem_config. I think that what we need is > >> a way of specifying cell config outside of nvmem providers in some > >> kind of structures. These tables would reference the provider by name > >> and define the cells. Then we would have an additional lookup > >> structure which would associate the consumer (by dev_id and con_id, > >> where dev_id could optionally be NULL and where we would fall back to > >> using con_id only) and the nvmem provider + cell together. Similarly > >> to how GPIO consumers are associated with the gpiochip and hwnum. How > >> does it sound? > > > > Yes, sounds good. > > > > Correct me if am wrong! > > You should be able to add the new cells using struct nvmem_cell_info and add > > them to particular provider using nvmem_add_cells(). > > > > Sounds like thats exactly what nvmem_add_lookup_table() would look like. > > > > We should add new nvmem_device_cell_get(nvmem, conn_id) which would return > > nvmem cell which is specific to the provider. This cell can be used by the > > machine driver to read/write. > > Except that we could do it lazily - when the nvmem provider actually > gets registered instead of doing it right away and risking that the > device isn't even there yet. And again, I agree with you. That's basically what lookup tables are meant for: defining resources that are supposed to be attached to a device when it's registered to a subsystem. > > > > >>>> > >>>> BTW: of_nvmem_cell_get() seems to always allocate an nvmem_cell > >>>> instance even if the cell for this node was already added to the nvmem > >>>> device. > >>> > >>> > >>> I hope you got the reason why of_nvmem_cell_get() always allocates new > >>> instance for every get!! > >> > >> > >> > >> I admit I didn't test it, but just from reading the code it seems like > >> in nvmem_cell_get() for DT-users we'll always get to > >> of_nvmem_cell_get() and in there we always end up calling line 873: > >> cell = kzalloc(sizeof(*cell), GFP_KERNEL); > >> > > That is correct, this cell is created when we do a get and release when we > > do a put(). > > > > Shouldn't we add the cell to the list, and check first if it's there > and only create it if not? Or even better: create the cells at registration time so that the search code is the same for both DT and non-DT cases. Only the registration would differ (with one path parsing the DT, and the other one searching for nvmem cells defined with a nvmem-provider-lookup table).
