linux-kernel - Re: [PATCH] firmware: dmi_scan: Always show system identification string

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Date:   Tue, 13 Dec 2016 15:42:45 +0100
From:   Jean Delvare <jdelvare@...e.de>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Kefeng Wang <wangkefeng.wang@...wei.com>,
        Mark Rutland <mark.rutland@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] firmware: dmi_scan: Always show system identification
 string

On mar., 2016-12-13 at 14:25 +0000, Ard Biesheuvel wrote:
> On 12 December 2016 at 01:51, Kefeng Wang <wangkefeng.wang@...wei.com> wrote:
> >
> >
> > On 2016/12/9 22:55, Ard Biesheuvel wrote:
> >> On 9 December 2016 at 06:54, Kefeng Wang <wangkefeng.wang@...wei.com> wrote:
> >>> Let's keep consistent when print dmi_ids_string between SMBIOS 2.x
> >>> and SMBIOS 3.x, and always show the system identification string,
> >>> like Vendor, Product/Board name and BIOS infos.
> >>>
> >>
> >> Are you saying the printk(KERN_DEBUG) was inconsistent with the
> >> pr_debug() before?
> >
> > Yes, found it when check the boot dmesg on qemu, there is no print using pr_debug
> > with defconfig on ARM64( smbios3 present), but could shown with printk(KERN_DEBUG.
> >
> 
> That's interesting. I would assume pr_debug and printk(KERN_DEBUG) to
> behave identically ...

And you'd be wrong ;-)

>From include/linux/printk.h:

304 #if defined(CONFIG_DYNAMIC_DEBUG)
305 #include <linux/dynamic_debug.h>
306 
307 /* dynamic_pr_debug() uses pr_fmt() internally so we don't need it here */
308 #define pr_debug(fmt, ...) \
309         dynamic_pr_debug(fmt, ##__VA_ARGS__)
310 #elif defined(DEBUG)
311 #define pr_debug(fmt, ...) \
312         printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
313 #else
314 #define pr_debug(fmt, ...) \
315         no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
316 #endif

Which basically means that pr_debug() has no effect unless debugging is
actually enabled, while printk(KERN_DEBUG ...) is always printed by the
kernel (with a log level which may or may not make it to a specific
output.)


-- 
Jean Delvare
SUSE L3 Support