Re: [PATCH] lib/rendercopy_gen9: Setup Push constant pointer before sending BTP commands

From: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
To: Ben Widawsky <benjamin.widawsky@intel.com>
Cc: intel-gfx@lists.freedesktop.org, Mika Kuoppala <mika.kuoppala@intel.com>
Subject: Re: [PATCH] lib/rendercopy_gen9: Setup Push constant pointer before sending BTP commands
Date: Thu, 13 Aug 2015 10:33:00 +0300	[thread overview]
Message-ID: <1439451180.4312.12.camel@linux.intel.com> (raw)
In-Reply-To: <20150813013537.GA10075@intel.com>

Hi,

On ke, 2015-08-12 at 18:35 -0700, Ben Widawsky wrote:
> On Wed, Aug 12, 2015 at 03:10:18PM +0300, Joonas Lahtinen wrote:
> > On ke, 2015-08-12 at 12:26 +0100, Arun Siluvery wrote:
> > > From Gen9, by default push constant command is not committed to 
> > > the 
> > > shader unit
> > > untill the corresponding shader's BTP_* command is parsed. This 
> > > is 
> > > the
> > > behaviour when set shader is enabled. This patch updates the 
> > > batch to 
> > > follow
> > > this requirement otherwise it results in gpu hang.
> > > 
> > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89959
> > > 
> > > Set shader need to be disabled if legacy behaviour is required.
> > > 
> > > Cc: Ben Widawsky <benjamin.widawsky@intel.com>
> > > Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > > Cc: Mika Kuoppala <mika.kuoppala@intel.com>
> > > Signed-off-by: Arun Siluvery <arun.siluvery@linux.intel.com>
> > 
> > Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> > 
> 
> Repeating what I said on the mesa thread:
> Does anyone understand why this actually causes a hang on the IGT 
> test? I
> certainly don't. The docs are pretty clear that the constant command 
> is not
> committed until the BTP command, but I can't make any sense of how it 
> related to
> a GPU hang.
> 

Changing the order makes the hang go away and come back for sure, we've
all been experiencing that. System validation said it is a programming
restriction, so I'm not sure how relevant it is what goes wrong if it's
not followed. And the legacy mode bits were added to support the old
behavior of having the order like it has been previously, so I do not
see why question it without visibility to the actual RTL. And enabling
the legacy bits makes the hang go away, too.

If I had the RTL sources, then it would be more relevant to take
educated guesses as to why a set of hundreds of thousands of
transistors doesn't work as it should :) Without that, if it gets
stuck, it gets stuck.

Regards, Joonas

> [snip]
> 
> ---
> Ben Widawsky, Intel Open Source Technology Center
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