[RFC PATCH 1/3] drivers: amba: Updates to component identification for driver matching.

From: mike.leach@linaro.org (Mike Leach)
To: linux-arm-kernel@lists.infradead.org
Subject: [RFC PATCH 1/3] drivers: amba: Updates to component identification for driver matching.
Date: Wed, 21 Nov 2018 15:53:23 +0000	[thread overview]
Message-ID: <CAJ9a7ViFRUuZQnqvtEO-OOjSGY45e7vxgPn0cTC6wnZw9ij9xg@mail.gmail.com> (raw)
In-Reply-To: <AM6PR08MB36868BDA513BA392E01EDE9D86DA0@AM6PR08MB3686.eurprd08.prod.outlook.com>

Hi Al,

On Wed, 21 Nov 2018 at 14:25, Al Grant <Al.Grant@arm.com> wrote:
>
> > @devarch is defined as a 32 bit value. This is masked to widen / narrow
> > matching. By default the mask will be the ARCHID field - bits 15:0, selected in the
> > driver in the same way as the drivers currently have a mask for peripheral ID.
> > This ignores the architect and version fields as most CS component drivers
> > should handle differences.
>
> The architect field defines what the ARCHID field means (the ARCHID
> values are specific to each architect), it's not the same as the implementer
> field. You need to check both if you want to know what component driver
> to use. The correct mask for that is 0xfff0ffff.
>
> Selecting on ARCHID alone, would only be valid if you are requiring the
> architect always to be ARM (0x23b) and have already checked that.
>

This is a fair point - thought at present the peripheral ID matching
takes in the JDEC ID code of the component designer - in the ETM case
ARM (though without a JDEC continuation code check).
Given this field too is specified as "designer not implementer", it
seems logically unlikely that designer != architect.

If we did feel the need to alter the match value / mask values - this
happens in the CS driver code, not in this patch - so will need to be
addressed there.

Thanks

Mike

> Al
> IMPORTANT NOTICE: The contents of this email and any attachments are confidential and may also be privileged. If you are not the intended recipient, please notify the sender immediately and do not disclose the contents to any other person, use it for any purpose, or store or copy the information in any medium. Thank you.

-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK