Re: [PATCH V5 2/7] soc: qcom-geni-se: Add interconnect support to fix earlycon crash

From: Matthias Kaehlcke <mka@chromium.org>
To: Akash Asthana <akashast@codeaurora.org>
Cc: gregkh@linuxfoundation.org, agross@kernel.org,
	bjorn.andersson@linaro.org, wsa@the-dreams.de,
	broonie@kernel.org, mark.rutland@arm.com, robh+dt@kernel.org,
	linux-i2c@vger.kernel.org, linux-spi@vger.kernel.org,
	devicetree@vger.kernel.org, swboyd@chromium.org,
	mgautam@codeaurora.org, linux-arm-msm@vger.kernel.org,
	linux-serial@vger.kernel.org, dianders@chromium.org,
	evgreen@chromium.org, georgi.djakov@linaro.org
Subject: Re: [PATCH V5 2/7] soc: qcom-geni-se: Add interconnect support to fix earlycon crash
Date: Fri, 8 May 2020 12:14:54 -0700	[thread overview]
Message-ID: <20200508191454.GH4525@google.com> (raw)
In-Reply-To: <20200508175938.GB4525@google.com>

On Fri, May 08, 2020 at 10:59:38AM -0700, Matthias Kaehlcke wrote:
> Hi Akash,
> 
> overall this looks good to me, a few comments inline
> 
> On Fri, May 08, 2020 at 12:03:34PM +0530, Akash Asthana wrote:
> > QUP core clock is shared among all the SE drivers present on particular
> > QUP wrapper, the system will reset(unclocked access) if earlycon used after
> > QUP core clock is put to 0 from other SE drivers before real console comes
> > up.
> > 
> > As earlycon can't vote for it's QUP core need, to fix this add ICC
> > support to common/QUP wrapper driver and put vote for QUP core from
> > probe on behalf of earlycon and remove vote during earlycon exit call.
> > 
> > Signed-off-by: Akash Asthana <akashast@codeaurora.org>
> > Reported-by: Matthias Kaehlcke <mka@chromium.org>
> > ---
> > Change in V3:
> >  - Add geni_remove_earlycon_icc_vote API that will be used by earlycon
> >    exit function to remove ICC vote for earlyconsole.
> >  - Remove suspend/resume hook for geni-se driver as we are no longer
> >    removing earlyconsole ICC vote from system suspend, we are removing
> >    from earlycon exit.
> > 
> > Change in V4:
> >  - As per Matthias comment make 'earlycon_wrapper' as static structure.
> > 
> > Changes in V5:
> >  - Vote for core path only after checking whether "qcom_geni" earlycon is
> >    actually present or not by traversing over structure "console_drivers".
> > 
> >  drivers/soc/qcom/qcom-geni-se.c       | 63 +++++++++++++++++++++++++++++++++++
> >  drivers/tty/serial/qcom_geni_serial.c |  7 ++++
> >  include/linux/qcom-geni-se.h          |  2 ++
> >  3 files changed, 72 insertions(+)
> > 
> > diff --git a/drivers/soc/qcom/qcom-geni-se.c b/drivers/soc/qcom/qcom-geni-se.c
> > index 63403bf..66fe6f2 100644
> > --- a/drivers/soc/qcom/qcom-geni-se.c
> > +++ b/drivers/soc/qcom/qcom-geni-se.c

...

> > +#ifdef CONFIG_SERIAL_EARLYCON
> > +	if (console_drivers)
> 
> The loop should have curly braces ("use braces when a loop contains more than
> a single simple statement"), even though the compiler doesn't need them in
> this case. This is not a loop, but I was told by a maintainer that it equally
> applies, which makes sense.
> 
> You could avoid one level of indentation through:
> 
> if (!console_drivers)
> 	goto exit;
> 
> > +		for_each_console(bcon)

Actually the NULL check of 'console_drivers' is not needed:

#define for_each_console(con) \
        for (con = console_drivers; con != NULL; con = con->next)

see also:

commit caa72c3bc584bc28b557bcf1a47532a7a6f37e6f
Author: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Date:   Mon Feb 3 15:31:25 2020 +0200

    console: Drop double check for console_drivers being non-NULL