linux-kernel - Re: [PATCH 0/6] mailbox: arm_mhu: add support to use in doorbell mode

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Date:   Fri, 31 May 2019 11:21:08 -0500
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Arnd Bergmann <arnd@...db.de>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Brown <broonie@...nel.org>,
        Cristian Marussi <cristian.marussi@....com>
Subject: Re: [PATCH 0/6] mailbox: arm_mhu: add support to use in doorbell mode

Hi Sudeep,

On Fri, May 31, 2019 at 9:33 AM Sudeep Holla <sudeep.holla@....com> wrote:
>
> This is my another attempt to extend mailbox framework to support
> doorbell mode mailbox hardware. It also adds doorbell support to ARM
> MHU driver.
>
Nothing has really changed since the last time we discussed many months ago.
MHU remains same, and so are my points.

>
> Brief hardware description about MHU
> ====================================
>
> For each of the interrupt signals, the MHU drives the signal using a 32-bit
> register, with all 32 bits logically ORed together. The MHU provides a set of
> registers to enable software to SET, CLEAR, and check the STATUS of each of
> the bits of this register independently. The use of 32 bits for each interrupt
> line enables software to provide more information about the source of the
> interrupt.
>
"32 bits for each interrupt line"  =>  32 virtual channels or 32bit
data over one physical channel. And that is how the driver is
currently written.

> For example, each bit of the register can be associated with a type
> of event that can contribute to raising the interrupt.
>
Sure there can be a usecase where each bit is associated with an event
(virtual channel). As you said, this is just one example of how MHU
can be used. There are other ways MHU is used already.

Patch-2/6 looks good though. I will pick that up.

Thanks.