linux-kernel - Re: [PATCH v2 1/6] i3c: master: add enable(disable) hot join in sys entry

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Date:   Fri, 20 Oct 2023 15:45:28 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     "Zbigniew, Lukwinski" <zbigniew.lukwinski@...ux.intel.com>
Cc:     Frank Li <Frank.Li@....com>, alexandre.belloni@...tlin.com,
        conor.culhane@...vaco.com, imx@...ts.linux.dev, joe@...ches.com,
        linux-i3c@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/6] i3c: master: add enable(disable) hot join in sys
 entry

Hi Lukwinski,

zbigniew.lukwinski@...ux.intel.com wrote on Fri, 20 Oct 2023 10:55:27
+0200:

> On 10/18/2023 10:59 PM, Frank Li wrote:
> > Add hotjoin entry in sys file system allow user enable/disable hotjoin
> > feature.
> >
> > Add (*enable(disable)_hotjoin)() to i3c_master_controller_ops.
> > Add api i3c_master_enable(disable)_hotjoin();  
> 
> What is the use case for having HJ enable knob in sysfs available for user space other than for debug stuff? In other words, does user space really need to enable/disable HJ in runtime for other reason but debug? If it is only for debug maybe it  could be move to debugFS?

I don't think hotjoin should be considered as a debug feature. The
problem here is the power consumption which is higher if you enable
this feature (you need to keep everything clocked and ready to handle
an IBI) whereas if your design is "fixed" (more like an I2C bus) you
may save power by disabling this feature.

A module parameter does not fit here because it's a per-bus
configuration.

Thanks,
Miquèl