From mboxrd@z Thu Jan 1 00:00:00 1970 From: Imre Deak Date: Thu, 18 Mar 2010 08:52:39 +0000 Subject: Re: [PATCH v3 1/4] DSS2: OMAPFB: Add support for switching memory Message-Id: <20100318085239.GE30422@localhost> List-Id: References: <1267795582-21004-1-git-send-email-ville.syrjala@nokia.com> <20100317173407.GD30422@localhost> <20100317201425.GI18243@nokia.com> In-Reply-To: <20100317201425.GI18243@nokia.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: "Syrjala Ville (Nokia-D/Helsinki)" Cc: "Valkeinen Tomi (Nokia-D/Helsinki)" , "linux-fbdev@vger.kernel.org" , "linux-omap@vger.kernel.org" On Wed, Mar 17, 2010 at 09:14:25PM +0100, Syrjala Ville (Nokia-D/Helsinki) wrote: > On Wed, Mar 17, 2010 at 06:34:07PM +0100, Deak Imre (Nokia-D/Helsinki) wrote: > > Hi, > > > > couple of minor comments inlined. > > > > On Fri, Mar 05, 2010 at 02:26:19PM +0100, Syrjala Ville (Nokia-D/Helsinki) wrote: > > [...] > > > @@ -115,30 +184,57 @@ static int omapfb_setup_mem(struct fb_info *fbi, struct omapfb_mem_info *mi) > > > struct omapfb_info *ofbi = FB2OFB(fbi); > > > struct omapfb2_device *fbdev = ofbi->fbdev; > > > struct omapfb2_mem_region *rg; > > > - int r, i; > > > + int r = 0; > > > size_t size; > > > + int i; > > > > > > if (mi->type > OMAPFB_MEMTYPE_MAX) > > > return -EINVAL; > > > > > > size = PAGE_ALIGN(mi->size); > > > > > > - rg = &ofbi->region; > > > + rg = ofbi->region; > > > > > > - for (i = 0; i < ofbi->num_overlays; i++) { > > > - if (ofbi->overlays[i]->info.enabled) > > > - return -EBUSY; > > > + /* FIXME probably should be a rwsem ... */ > > > + mutex_lock(&rg->mtx); > > > + while (rg->ref) { > > > + mutex_unlock(&rg->mtx); > > > + schedule(); > > > + mutex_lock(&rg->mtx); > > > + } > > > > Yes, rwsem would mean no unnecessary scheduling and also make things > > clearer. > > Just tried it and seems to be mostly OK. We get lockdep checking as a > bonus. It didn't like setup_plane taking the same rwsem twice so I > added a check to see if the old and new regions are the same and just > lock once in that case. I thought rwsem was supposed to be OK with > read recursion but perhaps I was mitaken, or perhaps it's just lockdep > that's misbehaving. Ah ok, so it's not so obvious change. Nested read locks could really lead to a deadlock I think. A read lock will block if there is a write waiter in the queue to avoid write starvation.. --Imre