linux-kernel - Re: [PATCH v2 2/4] gpio: add viperboard gpio driver

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Date:	Tue, 16 Oct 2012 19:11:10 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Lars Poeschel <poeschel@...onage.de>
Cc:	Lars Poeschel <larsi@....tu-dresden.de>, sameo@...ux.intel.com,
	linux-kernel@...r.kernel.org, jic23@....ac.uk, khali@...ux-fr.org,
	ben-linux@...ff.org, w.sang@...gutronix.de,
	grant.likely@...retlab.ca
Subject: Re: [PATCH v2 2/4] gpio: add viperboard gpio driver

On Tue, Oct 16, 2012 at 3:38 PM, Lars Poeschel <poeschel@...onage.de> wrote:

> I had a look at regmap. This is interesting. But there is no regmap_bus
> implementation for usb. Are you pointing me in this direction ? ;-)

I was more thinking about whether it would be useful to use for this
MFD hub. So that for this MFD and it's children, you would use
regmap to:

1) Cache registers
2) Marshall the register read/writes across USB

I don't think it would be applicable for USB, as reading & writing registers
across USB is a pretty odd usecase. (IIRC using control transfers
right?)

> And it is not guaranteed, that this "address" and "value"
> are at the same position for other usb adapters. And this is getting even
> worse, if I think of reading values out of the viperboard...

I was mainly thinking about the Viperboard MFD complex.

> I would stay at the "cache" implementation I presented in the patch - this is
> too special.

You're special just like everybody else ;-)

But to be honest I haven't seen another USB device like this.
Which probably means that next week there will be dozens of them...

Yours,
Linus Walleij
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