linux-kernel - Re: [RFC PATCH 0/4] Drop custom logging

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Message-ID: <CAMEGJJ1oZ9XFw0609PrEABAgDwvapbc3hG4hJ=vBekUOepdiWw@mail.gmail.com>
Date:   Thu, 19 Jan 2023 13:47:44 +0000
From:   Phil Elwell <phil@...pberrypi.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Stefan Wahren <stefan.wahren@...e.com>,
        Umang Jain <umang.jain@...asonboard.com>,
        linux-media@...r.kernel.org, linux-staging@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org,
        linux-rpi-kernel@...ts.infradead.org,
        Florian Fainelli <f.fainelli@...il.com>,
        Adrien Thierry <athierry@...hat.com>,
        Dan Carpenter <error27@...il.com>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 0/4] Drop custom logging

On Thu, 19 Jan 2023 at 13:37, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> On Thu, Jan 19, 2023 at 01:31:12PM +0000, Phil Elwell wrote:
> > Hi all,
> >
> >
> > On Wed, 18 Jan 2023 at 17:55, Stefan Wahren <stefan.wahren@...e.com> wrote:
> > >
> > > Hi Umang,
> > >
> > > [add Phil]
> > >
> > > Am 18.01.23 um 12:58 schrieb Umang Jain:
> > > > Drop custom logging from the vchiq interface.
> > > > Mostly of them are replaced with dev_dbg and friends
> > > > and/or pr_info and friends.
> > > >
> > > > The debugfs log levels (in 4/4) are mapped to kernel
> > > > logs levels (coming from include/linux/kern_levels.h)
> > > > Would like some thoughts on it as I am not sure (hence
> > > > marking this is RFC)
> > > >
> > > >  From drivers/staging/vc04_services/interface/TODO:
> > > >
> > > > """
> > > > * Cleanup logging mechanism
> > > >
> > > > The driver should probably be using the standard kernel logging mechanisms
> > > > such as dev_info, dev_dbg, and friends.
> > >
> > > i don't have any experience with vchiq logging/debug. So i'm not sure if
> > > it's acceptable to lose the second log level dimension (like
> > > vchiq_arm_log_level) completely. Complex drivers like brcmfmac have a
> > > debug mask to avoid log spamming [1]. Maybe this is a compromise.
> > >
> > > Btw some loglevel locations has already been messed up during
> > > refactoring :-(
> > >
> > > [1] - drivers/net/wireless/broadcom/brcm80211/brcmfmac/debug.h
> > >
> > > > """
> > > >
> > > > Umang Jain (4):
> > > >    staging: vc04_services: vchiq_core: Drop custom logging
> > > >    staging: vc04_services: vchiq_arm: Drop custom logging
> > > >    staging: vc04_services: Drop custom logging
> > > >    staging: vc04_services: Drop remnants of custom logging
> > > >
> > > >   .../interface/vchiq_arm/vchiq_arm.c           | 151 +++---
> > > >   .../interface/vchiq_arm/vchiq_connected.c     |   5 +-
> > > >   .../interface/vchiq_arm/vchiq_core.c          | 479 ++++++++----------
> > > >   .../interface/vchiq_arm/vchiq_core.h          |  39 --
> > > >   .../interface/vchiq_arm/vchiq_debugfs.c       |  26 +-
> > > >   .../interface/vchiq_arm/vchiq_dev.c           |  78 ++-
> > > >   6 files changed, 329 insertions(+), 449 deletions(-)
> > > >
> >
> > Thanks for the nudge - this patch set hasn't yet made its way through
> > the sluggish rpi-kernel moderation.
> >
> > I understand the desire to remove the custom logging. I don't welcome
> > the loss of flexibility that comes with such a strategy
>
> What "loss of flexibility"?  You now have access to the full dynamic
> debugging facilities that all of the rest of the kernel has.  What is
> lacking?

Perhaps I've missed something, either in this patch set or the kernel
as a whole, but how is one supposed to set different logging levels on
different facilities within a driver/module, or even for the module as
a whole? I don't consider anything that requires reference to
individual lines in the source code to be a suitable replacement,
clever though it is.

> > , but I'm not
> > going to argue about it. What's harder to understand is the state that
> > this patchset leaves VCHIQ logging in. From what I can see, the
> > per-service logging control has gone, but the code still contains
> > macros that hint at something useful. Similarly, the debugfs support
> > is completely vestigial, giving the appearance of control while
> > actually achieving nothing.
>
> The debugfs files should also be removed if they don't do anything
> anymore.
>
> thanks,
>
> greg k-h