linux-kernel - Re: [PATCH 3/4] spi: bcm-mspi: Make BCMA optional to support non-BCMA chips

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Date:	Mon, 6 Apr 2015 12:36:11 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	Florian Fainelli <f.fainelli@...il.com>
Cc:	Andy Shevchenko <andy.shevchenko@...il.com>,
	Jonathan Richardson <jonathar@...adcom.com>,
	Mark Brown <broonie@...nel.org>,
	Dmitry Torokhov <dtor@...gle.com>,
	Anatol Pomazau <anatol@...gle.com>,
	Scott Branden <sbranden@...adcom.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-spi <linux-spi@...r.kernel.org>,
	bcm-kernel-feedback-list <bcm-kernel-feedback-list@...adcom.com>,
	devicetree <devicetree@...r.kernel.org>
Subject: Re: [PATCH 3/4] spi: bcm-mspi: Make BCMA optional to support non-BCMA chips

On 3 April 2015 at 19:52, Florian Fainelli <f.fainelli@...il.com> wrote:
> On 03/04/15 06:38, Andy Shevchenko wrote:
>> On Thu, Apr 2, 2015 at 10:23 PM, Jonathan Richardson
>> <jonathar@...adcom.com> wrote:
>>> The Broadcom MSPI controller is used on various chips. The driver only
>>> supported BCM53xx chips with BCMA (an AMBA bus variant). The driver is
>>> refactored to make BCMA optional and provides a new config for non BCMA
>>> systems.
>>
>>>  struct bcm_mspi {
>>> +       #ifdef CONFIG_SPI_BCMA_MSPI
>>>         struct bcma_device *core;
>>> -       struct spi_master *master;
>>> +       #endif
>>>
>>> +       void __iomem *base;
>>> +       struct spi_master *master;
>>>         size_t read_offset;
>>
>>> +       void (*mspi_write)(struct bcm_mspi *mspi, u16 offset, u32 value);
>>> +       u32 (*mspi_read)(struct bcm_mspi *mspi, u16 offset);
>>> +};
>>
>> To avoid ugly ifdefs I think better to split driver to core part and
>> the actual driver part, at the end you will have something like
>> mspi-core.c mspi-53xx.c mspi-whatever.c. Check for example spi-dw*.c
>
> Actually, I am really curious whether we need the special BCMA I/O
> accessors in the first place, cannot we just access the MSPI core on
> BCM53xx chips using regular MMIO? That would probably solve the
> "problem" entirely. Rafal, did you try this before?

It's a matter of choice between:
1) Using one design for all bcma users
2) Using one design for all bcm-mspi users
I believe no matter which one you choose, you'll break another one.

If you take a look at drivers/bcma/host_soc.c, you'll see we've there
core->io_addr. I guess you could use it as the base in bcm-mspi. That
of course will make you a bit less compatible with other bcma drivers
(skipping bcma R/W layer).


> As for splitting the driver into a "library" driver which is mostly
> independent from the bus and a bus-specific wrapper, I think BCMA is
> really the only special case here, which is why I suggested earlier to
> Jonathan that we might just prefer ifdefing things out instead of
> creating a separate layer just for BCMA.

I think you may be right, this #if for bcma shouldn't be that bad and
it shouldn't grow in the future.
Still, I'd like to get this patch split nicely to review independent changes.

-- 
Rafał
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