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

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Date: Wed, 7 Feb 2024 16:22:59 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
Cc: Abel Vesa <abel.vesa@...aro.org>, Stephen Boyd <sboyd@...nel.org>, 
	Matthias Brugger <matthias.bgg@...il.com>, Bjorn Andersson <andersson@...nel.org>, 
	Konrad Dybcio <konrad.dybcio@...aro.org>, 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 Wed, 7 Feb 2024 at 14:46, AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com> wrote:
>
> Il 07/02/24 12:45, Dmitry Baryshkov ha scritto:
> > On Wed, 7 Feb 2024 at 11:08, Abel Vesa <abel.vesa@...aro.org> wrote:
> >>
> >> 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.
> >
> > So, after the off-line discussion:
> > - add new compatible string for sm8450+
> > - register two spmi controller instances
>
> Well, I don't know about the actual hardware that you're trying to implement
> but, in my opinion, the "idea" of this series does actually make sense.
>
> The SPMI specification says that SPMI supports up to 4 masters, and up to
> 16 slaves.

So, that is my main question: whether this supports multiple masters
on a same bus or multiple buses. From the SoC pins description I
assume the latter is the case.

>
> Just my two cents.
>
> Cheers,
> Angelo
>
> > - drop the master-id from the SPMI interface
> > - optionally: think about having a new separate driver for v7 SPMI.
> >
> >>
> >>>
> >>>>
> >>>> 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
> >
> >
> >
>
>


-- 
With best wishes
Dmitry