linux-kernel - Re: [PATCH v3 6/7] venus: Make debug infrastructure more flexible

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Date:   Thu, 11 Jun 2020 11:52:17 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Joe Perches <joe@...ches.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Stanimir Varbanov <stanimir.varbanov@...aro.org>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-btrfs@...r.kernel.org, linux-acpi@...r.kernel.org,
        netdev@...r.kernel.org, Jason Baron <jbaron@...mai.com>
Subject: Re: [PATCH v3 6/7] venus: Make debug infrastructure more flexible

On Wed, Jun 10, 2020 at 11:42:43PM -0700, Joe Perches wrote:
> On Thu, 2020-06-11 at 08:26 +0200, Greg Kroah-Hartman wrote:
> > On Wed, Jun 10, 2020 at 01:23:56PM -0700, Joe Perches wrote:
> > > On Wed, 2020-06-10 at 12:49 -0700, Joe Perches wrote:
> > > > On Wed, 2020-06-10 at 15:37 +0200, Greg Kroah-Hartman wrote:
> > > > > Please work with the infrastructure we have, we have spent a lot of time
> > > > > and effort to make it uniform to make it easier for users and
> > > > > developers.
> > > > 
> > > > Not quite.
> > > > 
> > > > This lack of debug grouping by type has been a
> > > > _long_ standing issue with drivers.
> > > > 
> > > > > Don't regress and try to make driver-specific ways of doing
> > > > > things, that way lies madness...
> > > > 
> > > > It's not driver specific, it allows driver developers to
> > > > better isolate various debug states instead of keeping
> > > > lists of specific debug messages and enabling them
> > > > individually.
> > > 
> > > For instance, look at the homebrew content in
> > > drivers/gpu/drm/drm_print.c that does _not_ use
> > > dynamic_debug.
> > > 
> > > MODULE_PARM_DESC(debug, "Enable debug output, where each bit enables a debug category.\n"
> > > "\t\tBit 0 (0x01)  will enable CORE messages (drm core code)\n"
> > > "\t\tBit 1 (0x02)  will enable DRIVER messages (drm controller code)\n"
> > > "\t\tBit 2 (0x04)  will enable KMS messages (modesetting code)\n"
> > > "\t\tBit 3 (0x08)  will enable PRIME messages (prime code)\n"
> > > "\t\tBit 4 (0x10)  will enable ATOMIC messages (atomic code)\n"
> > > "\t\tBit 5 (0x20)  will enable VBL messages (vblank code)\n"
> > > "\t\tBit 7 (0x80)  will enable LEASE messages (leasing code)\n"
> > > "\t\tBit 8 (0x100) will enable DP messages (displayport code)");
> > > module_param_named(debug, __drm_debug, int, 0600);
> > > 
> > > void drm_dev_dbg(const struct device *dev, enum drm_debug_category category,
> > > 		 const char *format, ...)
> > > {
> > > 	struct va_format vaf;
> > > 	va_list args;
> > > 
> > > 	if (!drm_debug_enabled(category))
> > > 		return;
> > 
> > Ok, and will this proposal be able to handle stuff like this?
> 
> Yes, that's the entire point.

Currently I think there not enough "levels" to map something like
drm.debug to the new dyn dbg feature. I don't think it is intrinsic
but I couldn't find the bit of the code where the 5-bit level in struct
_ddebug is converted from a mask to a bit number and vice-versa.


Daniel.