linux-kernel - Re: [Spice-devel] [PATCH] drm/qxl: use qxl_num

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Message-ID: <621894308.48603466.1544105415949.JavaMail.zimbra@redhat.com>
Date:   Thu, 6 Dec 2018 09:10:15 -0500 (EST)
From:   Frediano Ziglio <fziglio@...hat.com>
To:     Gerd Hoffmann <kraxel@...hat.com>
Cc:     dri-devel@...ts.freedesktop.org, David Airlie <airlied@...hat.com>,
        David Airlie <airlied@...ux.ie>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <spice-devel@...ts.freedesktop.org>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <virtualization@...ts.linux-foundation.org>
Subject: Re: [Spice-devel] [PATCH] drm/qxl: use qxl_num_crtc directly

> 
> On Thu, Dec 06, 2018 at 07:53:10AM -0500, Frediano Ziglio wrote:
> > > 
> > > On Thu, Dec 06, 2018 at 05:59:25AM -0500, Frediano Ziglio wrote:
> > > > > 
> > > > > Just use qxl_num_crtc directly everywhere instead of using
> > > > > qdev->monitors_config->max_allowed.  Drops pointless indirection
> > > > > and also is less confusing.
> > > > > 
> > > > 
> > > > To me is MORE confusing, why comparing number of something with
> > > > another number? Previously code was comparing number of monitors
> > > > with number of monitors, not number of CRTs with number of
> > > > monitors.
> > > 
> > > Yes, spice/qxl and drm/kms use slightly different terminology.
> > > 
> > > drm crtc == qxl monitor.
> > > drm framebuffer == qxl surface.
> > > 
> > > You need to know that anyway when looking at the qxl ksm code.  We
> > > have function names like qxl_crtc_update_monitors_config().  I fail
> > > to see why that is a problem ...
> > > 
> > > cheers,
> > >   Gerd
> > 
> > I don't see any problem too but you are explaining to me
> > why your rationale "and also is less confusing" does not
> > stand.
> 
> Well, it's less confusing because it takes away an indirection (not
> because of the naming).
> 

It does not confuse me.

> qdev->monitors_config->max_allowed is effectively set by a module
> parameter.  So using the module parameter variable qxl_num_crtc
> directly is better IMO.  The kernel doesn't need to dereference pointers
> each time it needs the value, and when reading the code you don't have
> to trace where and why qdev->monitors_config->max_allowed is set.
> 

That should go to the commit message!
With that the patch is fine for me.

Maybe there's no much point on reusing the same structure used
inside QXLRom/QXLRam but this is OT for this patch.

> cheers,
>   Gerd
> 
> 

Frediano