linux-kernel - Re: [PATCH] RFC: add function for localbus address

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Message-ID: <20141022232021.GF27405@n2100.arm.linux.org.uk>
Date:	Thu, 23 Oct 2014 00:20:21 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	Grant Likely <grant.likely@...aro.org>,
	Stanimir Varbanov <svarbanov@...sol.com>,
	Rob Herring <rob.herring@...aro.org>,
	Arnd Bergmann <arnd@...db.de>, devicetree@...r.kernel.org,
	linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
	Mark Brown <broonie@...nel.org>,
	Lee Jones <lee.jones@...aro.org>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] RFC: add function for localbus address

On Wed, Oct 22, 2014 at 04:01:26PM -0700, Stephen Boyd wrote:
> Where did this end up? When we talked at Connect I think we settled on
> exploring a driver core specific API like dev_get_localbus_address()
> that calls of_get_localbus_address() for devices with an of_node and in
> the future it could call something like acpi_get_localbus_address() when
> there's an acpi_node. I believe the biggest concern is that we're making
> an API that is OF or platform bus specific when it doesn't need to be.
> Making a driver core specific API avoids this problem by making it bus
> agnostic.

Given how little information there is in the original patch as to exactly
what problem this is addressing, I could be getting the wrong end of the
stick here.

Is this about trying to have a way to obtain the bus local addresses
associated with CPU-view resources?

If so, how about looking towards PCI, which has had this problem for the
last 15+ years, where PCI bus addresses are not necessarily the same as
CPU physical addresses?

There, we don't end up with multiple addresses specified in resources.
We instead have a way to translate between resources and bus-local
addresses, which IMHO is far nicer and less error-prone than having to
specify the same information twice, once with an offset and once without.

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