linux-kernel - Re: [PATCH 2/3] ARM: sunxi: Add an ahci-platform compatible AHCI driver for the Allwinner SUNXi series of SoCs

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Date:	Fri, 6 Dec 2013 10:01:17 +0100
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Olliver Schinagl <oliver+list@...inagl.nl>,
	Oliver Schinagl <oliver@...inagl.nl>, grant.likely@...aro.org,
	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org, dev@...ux-sunxi.org,
	maxime.ripard@...e-electrons.com, ijc@...lion.org.uk,
	hdegoede@...hat.com, Richard Zhu <r65037@...escale.com>,
	Shawn Guo <shawn.guo@...aro.org>
Subject: Re: [PATCH 2/3] ARM: sunxi: Add an ahci-platform compatible AHCI
 driver for the Allwinner SUNXi series of SoCs

Dear Tejun Heo,

On Wed, 4 Dec 2013 08:23:12 -0500, Tejun Heo wrote:

> > But again, point me (for dummies ;) in the right direction and I'll
> > work on it with some help.
> 
> Richard and Shawn recently worked on ahci_imx.  Can you guys please
> talk with each other and figure out what can be done to share as much
> as possible among these new platform-specific drivers?  I'd really
> like to see the common things factored out as much as possible with
> only the actual hardware differences described for each device.

Also, please Cc me on such discussions. I have a pending AHCI platform
driver for another ARM SoC family. It is very similar to ahci_platform,
but needs to do a few more things that are SoC specific (map an
additional register area, and do some SoC-specific stuff with them).

For the moment, we're left with two approaches:

 * Do what Oliver did, where the ahci_<foo> driver will do its own
   SoC-specific stuff, and then will register an additional
   platform_device to trigger the ->probe() of the generic
   ahci_platform driver. I must say I don't really like this solution,
   since it involves having two platform_device registered for the same
   piece of hardware (one platform_device to trigger the ->probe of
   ahci_<foo>, and another one to trigger the ->probe of ahci_platform).

 * Duplicate in ahci_<foo> the (relatively small) amount of code that
   is present in ahci_platform.

>From my point of view, ahci_platform should be turned into a small
"library", that provides an API for ahci_<foo> drivers to 1/ do their
own custom stuff and 2/ do the common ahci_platform stuff.

This way we avoid the registration of two platform_device for the same
piece of hardware, and we avoid the duplication of code.

Want me to propose a RFC for this idea?

Best regards,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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