linux-kernel - Re: [PATCH 0/9] bus: brcmstb_gisb: add support for GISBv7 arbiter

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Date:   Fri, 24 Mar 2017 09:02:32 -0700
From:   Doug Berger <opendmb@...il.com>
To:     Mark Rutland <mark.rutland@....com>
Cc:     catalin.marinas@....com, robh+dt@...nel.org, will.deacon@....com,
        computersforpeace@...il.com, gregory.0xf0@...il.com,
        f.fainelli@...il.com, bcm-kernel-feedback-list@...adcom.com,
        wangkefeng.wang@...wei.com, james.morse@....com,
        vladimir.murzin@....com, panand@...hat.com, andre.przywara@....com,
        cmetcalf@...lanox.com, mingo@...nel.org,
        sandeepa.s.prabhu@...il.com, shijie.huang@....com,
        linus.walleij@...aro.org, treding@...dia.com, jonathanh@...dia.com,
        olof@...om.net, mirza.krak@...il.com, suzuki.poulose@....com,
        bgolaszewski@...libre.com, horms+renesas@...ge.net.au,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 0/9] bus: brcmstb_gisb: add support for GISBv7 arbiter

On 03/24/2017 08:03 AM, Mark Rutland wrote:
> On Fri, Mar 24, 2017 at 07:46:23AM -0700, Doug Berger wrote:
>> This patch set contains changes to enable the GISB arbiter driver
>> on the latest ARM64 architecture Set-Top Box chips from Broadcom.
>>
>> This driver relies on being able to hook the abort handlers of
>> the processor core that are triggered by bus error signals
>> generated by the GISB bus arbiter hardware found in BCM7XXX chips.
>
> Ugh; hardware generating asynchonous exceptions is hideous. I had hoped
> that such hardware was a thing of the past.
Yes, hope springs eternal :)

>
> Under what circumstances does the GISB bus arbiter generate these
> aborts?
Since the GISB bus generally uses buffered writes it can early ack the
CPU bus master before the arbitration error is detected.  This causes
the bus error to be seen as an asynchronous abort by the CPU.

>
> Mark.
>