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

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Date: Wed, 7 Feb 2024 15:57:56 +0100
From: neil.armstrong@...aro.org
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 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 07/02/2024 15:22, Dmitry Baryshkov wrote:
> 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.

This is clearly 2 separate physically separate busses, not 2 masters on the same bus.

We registers separate controllers for i2c, spi, 1w, ... in this case, why not here ?

Neil

> 
>>
>> 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
>>>
>>>
>>>
>>
>>
> 
>