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

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Message-ID: <ZcNIddeG6VHxBEOQ@linaro.org>
Date: Wed, 7 Feb 2024 11:08:05 +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 09:23:09, Dmitry Baryshkov wrote:
> On Wed, 7 Feb 2024 at 09:19, Abel Vesa <abel.vesa@...aro.org> wrote:
> >
> > 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.
> 
> struct spmi_controller is a controller for a single bus. Inside your
> device you have two SPMI buses, each can be controlled by its own
> struct spmi_controller. Just like devices that control multiple I2C,
> SPI or USB busses register a separate instance of the bus controller.

Well, this is what this patchset is trying to do in the generic part.
The SPMI controller supports multiple buses (HW-wise) and therefore SW
implementation shouldn't be tied to single bus requirement.

> 
> >
> > 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.
> 
> Buses, not just masters.
> 
> >
> > >
> > > >
> > > > 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
> 
> 
> 
> -- 
> With best wishes
> Dmitry