Re: [PATCH V3] MIPS: BCM47XX: Move NVRAM driver to the drivers/soc/

From: "Rafał Miłecki" <zajec5@gmail.com>
To: Paul Walmsley <paul@pwsan.com>
Cc: "linux-mips@linux-mips.org" <linux-mips@linux-mips.org>,
	Ralf Baechle <ralf@linux-mips.org>,
	Hauke Mehrtens <hauke@hauke-m.de>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Kumar Gala <galak@codeaurora.org>,
	Olof Johansson <olof@lixom.net>, Arnd Bergmann <arnd@arndb.de>,
	Sandeep Nair <sandeep_n@ti.com>,
	linux-soc@vger.kernel.org,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH V3] MIPS: BCM47XX: Move NVRAM driver to the drivers/soc/
Date: Thu, 27 Nov 2014 23:36:53 +0100	[thread overview]
Message-ID: <CACna6rwMjOfmnA-926udNx7jQHQ2JMnmiutQZkTxtJ85qmUw8A@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.02.1411271926560.1406@utopia.booyaka.com>

On 27 November 2014 at 20:56, Paul Walmsley <paul@pwsan.com> wrote:
> On Tue, 25 Nov 2014, Rafał Miłecki wrote:
>> I understand your arguments against drivers/soc/, but on the other hand
>> I have no idea where else this driver could go.
>
> After looking around the tree to find out where similar code is located,
> it looks like drivers/firmware is the right place.  These days,
> drivers/firmware is mainly used for drivers that parse EFI bootloader
> data, DMI data, that sort of thing.  Quite similar to the CFE-provided
> data that the bcm47xx-nvram code deals with.  So, by functional analogy,
> drivers/firmware appears to be the right place to stash this device
> data-probing code.
>
>> I guess DT is older than CFE, but Broadcom decided to invent own
>> solution called NVRAM anyway. This is a bit messy, because it actually
>> stores hardware details (CPU, RAM, switch) as well as user settings
>> (e.g. LEDs behavior). I can't say why Broadcom decided to implement it
>> this way.
>
> Yep, based on what the other drivers in drivers/firmware are used for, I
> think drivers/firmware is the right place for the CFE parsing code.

The problem is I can't find MAINTAINER of the drivers/firmware/. Is
there someone responsible for that? Some mailing list maybe? Who could
give us an ACK to move bcm47xx_nvram there?

>> > It sounds to me like this code is a combination of three
>> > pieces:
>> >
>> > 1. code that autoprobes the size of the "nvram" partition in the Broadcom
>> > platform flash, by reading various locations in the MMIO flash aperture,
>> > configured by some other system entity
>>
>> That's right, on MIPS we simply detect flash type (drivers/ssb &
>> driver/bcma) and using that we init NVRAM passing memory offset where
>> the flash is mapped.
>
> OK.
>
> So (as a side issue), I would suggest that when you move this code out of
> arch/mips, the MIPS-isms in it should be removed, like KSEG1ADDR(), etc.,
> and replaced by the standard ioremap()-type approach.  After all, Broadcom
> could build CFE for ARM, and then we'd want to use this same code to parse
> the CFE-provided data.
>
> Also I would suggest getting rid of the #ifdefs for the flash type, and
> probing it dynamically instead.  The flash setup code under drivers/ssb/
> and drivers/bcma/ sets up platform_devices for the flash, right?  If so
> then it would be best if this code could run after the bus setup code,
> query the Linux device model for the type of platform flash in use, and
> then extract the appropriate address space to probe from that data.

I'm pretty sure you look at some old version of arch/bcm47xx/nvram.c.
I wouldn't dare to move such a MIPS-focused driver to some common
place ;)

Please check for the version of nvram.c in Ralf's upstream-sfr tree. I
think you'll like it much more. Hopefully you will even consider it
ready for moving to the drivers/firmware/ or whatever :)

-- 
Rafał