Re: [PATCH 14/17] media: atomisp: pci: Remove remaining instance of call to trace_printk

[Tsuchiya Yuto]

<Adding back people/list to Cc>

On Tue, 2021-10-26 at 09:32 +0100, Mauro Carvalho Chehab wrote:
> Em Mon, 18 Oct 2021 01:19:54 +0900
> Tsuchiya Yuto <kitakar@xxxxxxxxx> escreveu:
> 
> > (patch based on intel-aero kernel patch:
> >  https://github.com/intel-aero/meta-intel-aero-base/commit/26fc9fe5030b63bc9dcf0b5f32981948911ca272)
> > 
> > Here is the original commit message from the aforementioned patch:
> > 
> > 	From 26fc9fe5030b63bc9dcf0b5f32981948911ca272 Mon Sep 17 00:00:00 2001
> > 	From: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
> > 	Date: Fri, 7 Jul 2017 14:23:53 -0700
> > 	Subject: [PATCH] linux-yocto: Remove remaining instance of call to
> > 	 trace_printk
> > 
> > 	It's not sufficient to leave trace_printk() out of "normal call chains" since
> > 	the way trace infrastructure works is that it will allocate the trace_printk
> > 	buffers if the symbol is there (by using a separate section for the function
> > 	and checking if __start_* and __stop_* symbols are different.
> > 
> > 	Therefore, even if the default value for the param tells the module to use
> > 	printk(), just the fact that it can be changed to trace_printk() means the
> > 	initialization code will be called.
> > 
> > The trace_printk() was replaced by pr_info() on commit 3d81099c75a6
> > ("media: atomisp: Replace trace_printk by pr_info") for the upstreamed
> > atomisp, too. However, as the aforementioned commit message says, there
> > is still a remaining instance. This causes the "trace_printk() being
> > used" kernel warning message to still appear on the first driver load.
> > 
> > Based on the aforementioned patch, this patch removes the call to
> > ftrace_vprintk(). This removes that kernel warning.
> > 
> > In addition to this, this patch also removes the following now unused
> > things:
> > 
> >     - now empty atomisp_css2_dbg_ftrace_print()
> >     - trace_printk option from dbg_func kernel parameter
> 
> This patch is incomplete. I mean, if the idea is to drop support for
> trace, dbg_func parameter becomes obsolete, and a lot of code can be
> dropped/cleaned.

I left __set_css_print_env() and dbg_func module parameter intentionally
because there is still the option "non", which means do not use any
function to log. Yes, I don't know if it's really useful since the module
parameter dbg_level=0 (this is the default value) means no debug output.

However, they (those who originally wrote atomisp) added the option "non"
anyway. So, I thought there is a use case for this.

If everyone thinks it's useless, I can additionally remove them. In this
case, indeed a lot of code may be additionally removed (I haven't checked
yet).

> That's said, I don't see a good reason to drop it, at least while
> this driver is not 100%.

This driver is not 100% yet, but at least it can capture images now
(at least on ISP2401). So, I thought this is the right time to remove
it when I wrote this patch.

But yes, we don't necessarily have to drop it. The other idea is hide
it by default using a macro, and still can be enabled by manual edit.
Here is the example from drivers/usb/dwc2/core.h:

        49-/*
        50- * Suggested defines for tracers:
        51- * - no_printk:    Disable tracing
        52- * - pr_info:      Print this info to the console
        53- * - trace_printk: Print this info to trace buffer (good for verbose logging)
        54- */
        55-
        56:#define DWC2_TRACE_SCHEDULER		no_printk
        57:#define DWC2_TRACE_SCHEDULER_VB		no_printk
        58-
        59-/* Detailed scheduler tracing, but won't overwhelm console */
        60-#define dwc2_sch_dbg(hsotg, fmt, ...)					\
        61:	DWC2_TRACE_SCHEDULER(pr_fmt("%s: SCH: " fmt),			\
        62-			     dev_name(hsotg->dev), ##__VA_ARGS__)
        63-
        64-/* Verbose scheduler tracing */
        65-#define dwc2_sch_vdbg(hsotg, fmt, ...)					\
        66:	DWC2_TRACE_SCHEDULER_VB(pr_fmt("%s: SCH: " fmt),		\
        67-				dev_name(hsotg->dev), ##__VA_ARGS__)

with using pr_info by default for atomisp (the parameter dbg_level is
0 by default, so still no output by default). If this sounds OK, I'd
like to try this way.

> > 
> > Signed-off-by: Tsuchiya Yuto <kitakar@xxxxxxxxx>
> > ---
> >  .../staging/media/atomisp/pci/atomisp_compat_css20.c   | 10 ----------
> >  drivers/staging/media/atomisp/pci/atomisp_v4l2.c       |  4 ++--
> >  2 files changed, 2 insertions(+), 12 deletions(-)
> > 
> > diff --git a/drivers/staging/media/atomisp/pci/atomisp_compat_css20.c b/drivers/staging/media/atomisp/pci/atomisp_compat_css20.c
> > index 99a632f33d2d..d81d55c6f1fa 100644
> > --- a/drivers/staging/media/atomisp/pci/atomisp_compat_css20.c
> > +++ b/drivers/staging/media/atomisp/pci/atomisp_compat_css20.c
> > @@ -159,13 +159,6 @@ static void atomisp_css2_hw_load(hrt_address addr, void *to, uint32_t n)
> >  	spin_unlock_irqrestore(&mmio_lock, flags);
> >  }
> >  
> > -static int  __printf(1, 0) atomisp_css2_dbg_ftrace_print(const char *fmt,
> > -							 va_list args)
> > -{
> > -	ftrace_vprintk(fmt, args);
> > -	return 0;
> > -}
> > -
> >  static int  __printf(1, 0) atomisp_vprintk(const char *fmt, va_list args)
> >  {
> >  	vprintk(fmt, args);
> > @@ -860,9 +853,6 @@ static inline int __set_css_print_env(struct atomisp_device *isp, int opt)
> >  	if (opt == 0)
> >  		isp->css_env.isp_css_env.print_env.debug_print = NULL;
> >  	else if (opt == 1)
> > -		isp->css_env.isp_css_env.print_env.debug_print =
> > -		    atomisp_css2_dbg_ftrace_print;
> > -	else if (opt == 2)
> >  		isp->css_env.isp_css_env.print_env.debug_print = atomisp_vprintk;
> >  	else
> >  		ret = -EINVAL;
> > diff --git a/drivers/staging/media/atomisp/pci/atomisp_v4l2.c b/drivers/staging/media/atomisp/pci/atomisp_v4l2.c
> > index f5362554638e..720963156d24 100644
> > --- a/drivers/staging/media/atomisp/pci/atomisp_v4l2.c
> > +++ b/drivers/staging/media/atomisp/pci/atomisp_v4l2.c
> > @@ -87,10 +87,10 @@ module_param(dbg_level, int, 0644);
> >  MODULE_PARM_DESC(dbg_level, "debug message level (default:0)");
> >  
> >  /* log function switch */
> > -int dbg_func = 2;
> > +int dbg_func = 1;
> >  module_param(dbg_func, int, 0644);
> >  MODULE_PARM_DESC(dbg_func,
> > -		 "log function switch non/trace_printk/printk (default:printk)");
> > +		 "log function switch non/printk (default:printk)");
> >  
> >  int mipicsi_flag;
> >  module_param(mipicsi_flag, int, 0644);