linux-kernel - Re: [PATCH v1] regmap: introduce value tracing for regmap bulk operations

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Date:   Fri, 19 Aug 2022 15:38:27 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Dmitry Rokosov <DDRokosov@...rdevices.ru>,
        gregkh@...uxfoundation.org, rafael@...nel.org, jic23@...nel.org,
        "linux@...musvillemoes.dk>" <linux@...musvillemoes.dk>,
        tglx@...utronix.de, andy.shevchenko@...il.com,
        kernel <kernel@...rdevices.ru>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] regmap: introduce value tracing for regmap bulk
 operations

On Fri, Aug 19, 2022 at 03:25:44PM +0100, Marc Zyngier wrote:
> On 2022-08-18 16:43, Mark Brown wrote:
> > On Thu, Aug 18, 2022 at 02:49:20PM +0100, Marc Zyngier wrote:

> > > I don't care much about regmap as a MMIO backend, but it strikes me as
> > > odd that you end up with multiple ways of logging the same stuff (with
> > > a memcpy in the middle of it).

> > > Why can't this be done with a small amount of trace post-processing?

> > At the minute we don't put the actual data for the bulk transfers into
> > the trace so the information simply isn't there.

> But isn't that what this patch should do?

I'd imagine so based on a quick glance at the description, I've not
actually reviewed it yet, but in that case I'm not sure what your
concern is here?

> We also have recently merged the CONFIG_TRACE_MMIO_ACCESS which
> already dumps all sort of MMIO crap^Winformation.

Yes, that'd also cover it for MMIO based regmaps when enabled but
obviously other buses exist and can also be accessed via regmap.

> Surely there should be a more common approach to this.

There's an argument for tracing at each abstraction layer since they're
generally all doing *something*, people will look to the layer they're
accessing and for things like tracing register accesses with buses like
I2C and SPI regmap is adding the register semantics on top of a bus
that's just a byte stream.  Even on buses with a native concept of an
address there's stuff like paging which might be added on depending on
the device.  They should probably all follow a similar pattern but I'm
not sure we can do everything at once.

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