linux-kernel - Re: [PATCH 03/11] dt-bindings: interrupt-controller: RISC-V PLIC documentation

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Date:   Thu, 9 Aug 2018 11:19:51 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Christoph Hellwig <hch@....de>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Palmer Dabbelt <palmer@...belt.com>, atish.patra@....com,
        Thomas Gleixner <tglx@...utronix.de>,
        Jason Cooper <jason@...edaemon.net>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org, Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <anup@...infault.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-riscv@...ts.infradead.org, Stafford Horne <shorne@...il.com>
Subject: Re: [PATCH 03/11] dt-bindings: interrupt-controller: RISC-V PLIC
 documentation

On 08/08/18 17:57, Christoph Hellwig wrote:
> On Wed, Aug 08, 2018 at 05:47:40PM +0100, Marc Zyngier wrote:
>> The original GIC driver deals with 2.5 revisions of the architecture
>> (yes, there was something pre-GICv1...), and implementers have been
>> creative to the extreme. Still, we could have done without most of these
>> compat strings. Hindsight and all that jazz.
>>
>> GICv3 is a much more controlled architecture, and although people have
>> come up with a number of turds masquerading as implementations, it has
>> never been bad enough to mandate a different set of compat strings.
>> Also, you cannot describe that kind of stuff in ACPI, and we need to
>> support both, so we've come up with different ways of handling this.
> 
> So the claim from SiFive is that all their current plic blocks are
> the same.  Based on that I'd be really tempted to just match for
> sifive,plic (or sifive,plic1 as suggested by them), but also require
> each device to actually provide a board specific compatible string,
> just in case that something goes wrong.  Which I suspect is what you
> are doing with GICv3, right?

We do it slightly differently:

Each GICv3 implementation has a set of ID registers that uniquely
identifies the implementer and revision of the HW block. This allows us
to quirk individual implementations while only having a single matching
property, and be independent of a single firmware implementation (DT vs
ACPI).

We don't mandate anything at the board or even SoC level though (it
would quickly become unmanageable given the number of SOCs and devices).

	M.
-- 
Jazz is not dead. It just smells funny...