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From: Boris Brezillon <boris.brezillon@bootlin.com>
To: Bartosz Golaszewski <brgl@bgdev.pl>
Cc: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>,
	Andrew Lunn <andrew@lunn.ch>,
	linux-doc <linux-doc@vger.kernel.org>,
	Sekhar Nori <nsekhar@ti.com>,
	Bartosz Golaszewski <bgolaszewski@baylibre.com>,
	linux-i2c <linux-i2c@vger.kernel.org>,
	Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
	Rob Herring <robh@kernel.org>,
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	Richard Weinberger <richard@nod.at>,
	Russell King <linux@armlinux.org.uk>,
	Marek Vasut <marek.vasut@gmail.com>,
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	"David S . Miller" <davem@davemloft.net>
Subject: Re: [PATCH v2 01/29] nvmem: add support for cell lookups
Date: Tue, 28 Aug 2018 16:53:09 +0200
Message-ID: <20180828165309.0594ae13@bbrezillon> (raw)
In-Reply-To: <CAMRc=MeALxpyBQhWxGPt9BubO_ZwKGih1d8zhRzFYZ0+3kHFAA@mail.gmail.com>

On Tue, 28 Aug 2018 16:41:04 +0200
Bartosz Golaszewski <brgl@bgdev.pl> wrote:

> 2018-08-28 15:45 GMT+02:00 Srinivas Kandagatla <srinivas.kandagatla@linaro.org>:
> >
> >
> > On 28/08/18 12:56, Bartosz Golaszewski wrote:  
> >>
> >> 2018-08-28 12:15 GMT+02:00 Srinivas Kandagatla
> >> <srinivas.kandagatla@linaro.org>:  
> >>>
> >>>
> >>> 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).

  parent reply index

Thread overview: 92+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-10  8:04 [PATCH v2 00/29] at24: remove at24_platform_data Bartosz Golaszewski
2018-08-10  8:04 ` [PATCH v2 01/29] nvmem: add support for cell lookups Bartosz Golaszewski
2018-08-24 15:08   ` Boris Brezillon
2018-08-24 15:27     ` Andrew Lunn
2018-08-25  6:27       ` Boris Brezillon
2018-08-27  8:56         ` Bartosz Golaszewski
2018-08-27  9:00           ` Boris Brezillon
2018-08-27 13:37             ` Bartosz Golaszewski
2018-08-27 14:01               ` Boris Brezillon
2018-08-28 10:15               ` Srinivas Kandagatla
2018-08-28 11:56                 ` Bartosz Golaszewski
2018-08-28 13:45                   ` Srinivas Kandagatla
2018-08-28 14:41                     ` Bartosz Golaszewski
2018-08-28 14:48                       ` Srinivas Kandagatla
2018-08-28 14:53                       ` Boris Brezillon [this message]
2018-08-28 15:09                         ` Srinivas Kandagatla
2018-08-10  8:04 ` [PATCH v2 02/29] Documentation: nvmem: document lookup entries Bartosz Golaszewski
2018-08-31 20:30   ` Brian Norris
2018-09-01 13:11     ` Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 03/29] nvmem: add a notifier chain Bartosz Golaszewski
2018-08-10  8:33   ` Srinivas Kandagatla
2018-08-10  8:05 ` [PATCH v2 04/29] nvmem: provide nvmem_dev_name() Bartosz Golaszewski
2018-08-10  8:10   ` Srinivas Kandagatla
2018-08-10  8:05 ` [PATCH v2 05/29] nvmem: remove the name field from struct nvmem_device Bartosz Golaszewski
2018-08-10  8:33   ` Srinivas Kandagatla
2018-08-10  8:05 ` [PATCH v2 06/29] mtd: Add support for reading MTD devices via the nvmem API Bartosz Golaszewski
2018-08-17 16:27   ` Boris Brezillon
2018-08-19 11:31     ` Alban
2018-08-19 16:46       ` Boris Brezillon
2018-08-20 10:43         ` Srinivas Kandagatla
2018-08-20 18:20           ` Boris Brezillon
2018-08-20 18:50             ` Bartosz Golaszewski
2018-08-20 19:06               ` Boris Brezillon
2018-08-20 21:27             ` Alban
2018-08-21  5:07               ` Boris Brezillon
2018-08-21  9:50             ` Srinivas Kandagatla
2018-08-21  9:56               ` Boris Brezillon
2018-08-21 10:11                 ` Srinivas Kandagatla
2018-08-21 10:43                   ` Boris Brezillon
2018-08-21 11:39               ` Alban
2018-08-21 12:00                 ` Srinivas Kandagatla
2018-08-21 13:01                   ` Boris Brezillon
2018-08-23 10:29                     ` Alban
2018-08-24 14:39                       ` Boris Brezillon
2018-08-28 10:20                       ` Srinivas Kandagatla
2018-08-20 22:53         ` Alban
2018-08-21  5:44           ` Boris Brezillon
2018-08-21  9:38             ` Srinivas Kandagatla
2018-08-21 11:31               ` Boris Brezillon
2018-08-21 13:34                 ` Srinivas Kandagatla
2018-08-21 13:37                   ` Srinivas Kandagatla
2018-08-21 13:57                     ` Boris Brezillon
2018-08-21 12:27             ` Alban
2018-08-21 12:57               ` Boris Brezillon
2018-08-21 13:57                 ` Alban
2018-08-21 14:26                   ` Boris Brezillon
2018-08-21 14:33                     ` Srinivas Kandagatla
2018-08-10  8:05 ` [PATCH v2 07/29] ARM: davinci: dm365-evm: use nvmem lookup for mac address Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 08/29] ARM: davinci: dm644-evm: " Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 09/29] ARM: davinci: dm646x-evm: " Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 10/29] ARM: davinci: da830-evm: " Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 11/29] ARM: davinci: mityomapl138: add nvmem cells lookup entries Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 12/29] ARM: davinci: da850-evm: use nvmem lookup for mac address Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 13/29] ARM: davinci: da850-evm: remove unnecessary include Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 14/29] net: simplify eth_platform_get_mac_address() Bartosz Golaszewski
2018-08-10 14:39   ` Andy Shevchenko
2018-08-10 16:17     ` Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 15/29] net: split eth_platform_get_mac_address() into subroutines Bartosz Golaszewski
2018-08-31 19:54   ` Brian Norris
2018-08-10  8:05 ` [PATCH v2 16/29] net: add support for nvmem to eth_platform_get_mac_address() Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 17/29] net: davinci_emac: use eth_platform_get_mac_address() Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 18/29] ARM: davinci: da850-evm: remove dead MTD code Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 19/29] ARM: davinci: mityomapl138: don't read the MAC address from machine code Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 20/29] ARM: davinci: dm365-evm: use device properties for at24 eeprom Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 21/29] ARM: davinci: da830-evm: " Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 22/29] ARM: davinci: dm644x-evm: " Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 23/29] ARM: davinci: dm646x-evm: " Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 24/29] ARM: davinci: sffsdr: fix the at24 eeprom device name Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 25/29] ARM: davinci: sffsdr: use device properties for at24 eeprom Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 26/29] ARM: davinci: remove dead code related to MAC address reading Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 27/29] ARM: davinci: mityomapl138: use nvmem notifiers Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 28/29] ARM: davinci: mityomapl138: use device properties for at24 eeprom Bartosz Golaszewski
2018-08-10  8:05 ` [PATCH v2 29/29] eeprom: at24: kill at24_platform_data Bartosz Golaszewski
2018-08-10  8:41 ` [PATCH v2 00/29] at24: remove at24_platform_data Srinivas Kandagatla
2018-08-31 19:46 ` Brian Norris
2018-10-03 20:15   ` Bartosz Golaszewski
2018-10-03 20:30     ` Lukas Wunner
2018-10-03 21:04     ` Florian Fainelli
2018-10-04 11:06       ` Bartosz Golaszewski
2018-10-04 13:58         ` Arnd Bergmann
2018-10-04 14:35           ` Sowmini Varadhan
2018-10-04 14:38             ` Arnd Bergmann

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