linux-kernel - Re: [PATCH 6/6] staging: fsl-mc: Changed version matching rules for MC object drivers

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Date:	Thu, 09 Apr 2015 01:11:04 +0200
From:	Alexander Graf <agraf@...e.de>
To:	"J. German Rivera" <German.Rivera@...escale.com>,
	gregkh@...uxfoundation.org, arnd@...db.de,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
CC:	stuart.yoder@...escale.com, Kim.Phillips@...escale.com,
	scottwood@...escale.com, bhamciu1@...escale.com,
	R89243@...escale.com, bhupesh.sharma@...escale.com,
	nir.erez@...escale.com, richard.schmitt@...escale.com
Subject: Re: [PATCH 6/6] staging: fsl-mc: Changed version matching rules for
 MC object drivers

On 03/27/2015 10:01 PM, J. German Rivera wrote:
> Before this change, we were requiring a complete version match (major and
> minor version numbers) between MC objects and corresponding drivers, to
> allow MC objects to be bound to their drivers. We realized that a mismatch
> in minor version numbers should be tolerated, as long as the major version
> numbers match. This allows the driver to decide what to do in the minor
> version mismatch case. For example, a driver may decide to run with
> downgraded functionality if the MC firmware object has older minor version
> number than the driver. Also, a driver with older minor version than the
> MC firmware object may decide to run even though it cannot use newer
> functionality of the MC object.
>
> As part of this change, the dpmng Flib version was also updated
> to match the latest MC firmware version.
>
> Signed-off-by: J. German Rivera <German.Rivera@...escale.com>

I think this is a step into the right direction, but you really don't 
want to match only when the minor equals. Usually you'd like something like

   if (cur_minor > max_minor) {
     dev_warn("Unknown version %d.%d of fsl-mc detected. Please update 
your kernel if you encounter problems.")
   }

but always assume that cur_minor < max_minor works. In cases where the 
protocol did change between minors, add code to support the older minors 
as well.


Alex

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