linux-kernel - Re: [PATCH RFC 1/2] spmi: Add support for multi-master

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Message-ID: <ZcMvFtAwQQjAZhk6@linaro.org>
Date: Wed, 7 Feb 2024 09:19:50 +0200
From: Abel Vesa <abel.vesa@...aro.org>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Stephen Boyd <sboyd@...nel.org>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Bjorn Andersson <andersson@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-arm-msm@...r.kernel.org, linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH RFC 1/2] spmi: Add support for multi-master

On 24-02-07 01:55:39, Dmitry Baryshkov wrote:
> On Wed, 7 Feb 2024 at 01:34, Abel Vesa <abel.vesa@...aro.org> wrote:
> >
> > Some newer SPMI controllers support multiple bus masters.
> > Such a master can control multiple slave devices. The generic
> > framework needs to be able to pass on the master id to the
> > controller-specific driver. So do that. The framework will
> > check if the devicetree child nodes are actually bus masters
> > and will register the devices for each master. The legacy
> > approach will still be supported for backwards compatibility.
> 
> Please remind me, are those two actual bus musters driving a single
> bus in parallel or two SPMI buses being handled by a single device? In
> the latter case this implementation is incorrect. There should be
> multiple spmi_controller instances, one for each bus. Allocate them in
> a loop and set ctrl->dev.of_node after allocating.

It's two SPMI buses (two sets of wires) handled by the same controller,
HW-wise.

If we register two spmi controllers with the kernel framework, it will
be HW inaccurate, because there is just one controller which has
multiple masters.

I'm not saying it might not work. But, to me, it looks more like a hack.

Basically, we would be mapping HW bus masters to kernel controllers.

> 
> >
> > Signed-off-by: Abel Vesa <abel.vesa@...aro.org>
> > ---
> >  drivers/spmi/spmi-mtk-pmif.c |  6 ++--
> >  drivers/spmi/spmi-pmic-arb.c | 10 +++---
> >  drivers/spmi/spmi.c          | 76 ++++++++++++++++++++++++++++++--------------
> >  include/linux/spmi.h         | 10 +++---
> >  4 files changed, 67 insertions(+), 35 deletions(-)
> 
> -- 
> With best wishes
> Dmitry