From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ingo Molnar Subject: Re: [PATCH v2 2/2] x86/mm/pat, drivers/media/ivtv: move pat warn and replace WARN() with pr_warn() Date: Mon, 29 Jun 2015 08:55:05 +0200 Message-ID: <20150629065505.GB17509@gmail.com> References: <1435166600-11956-1-git-send-email-mcgrof@do-not-panic.com> <1435166600-11956-3-git-send-email-mcgrof@do-not-panic.com> <20150625065147.GB5339@gmail.com> <20150625173847.GH3005@wotan.suse.de> <20150626084546.GD26303@gmail.com> <1435322161.2713.10.camel@localhost> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1435322161.2713.10.camel@localhost> Sender: linux-media-owner@vger.kernel.org To: Andy Walls Cc: "Luis R. Rodriguez" , Hyong-Youb Kim , Andy Walls , benh@kernel.crashing.org, "Luis R. Rodriguez" , bp@suse.de, mchehab@osg.samsung.com, dledford@redhat.com, fengguang.wu@intel.com, linux-media@vger.kernel.org, linux-rdma@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-rdma@vger.kernel.org * Andy Walls wrote: > On Fri, 2015-06-26 at 10:45 +0200, Ingo Molnar wrote: > > * Luis R. Rodriguez wrote: > > > > > On Thu, Jun 25, 2015 at 08:51:47AM +0200, Ingo Molnar wrote: > > > > > > > > * Luis R. Rodriguez wrote: > > > > > > > > > From: "Luis R. Rodriguez" > > > > > > > > > > On built-in kernels this warning will always splat as this is part > > > > > of the module init. Fix that by shifting the PAT requirement check > > > > > out under the code that does the "quasi-probe" for the device. This > > > > > device driver relies on an existing driver to find its own devices, > > > > > it looks for that device driver and its own found devices, then > > > > > uses driver_for_each_device() to try to see if it can probe each of > > > > > those devices as a frambuffer device with ivtvfb_init_card(). We > > > > > tuck the PAT requiremenet check then on the ivtvfb_init_card() > > > > > call making the check at least require an ivtv device present > > > > > before complaining. > > > > > > > > > > Reported-by: Fengguang Wu [0-day test robot] > > > > > Signed-off-by: Luis R. Rodriguez > > > > > --- > > > > > drivers/media/pci/ivtv/ivtvfb.c | 15 +++++++++------ > > > > > 1 file changed, 9 insertions(+), 6 deletions(-) > > > > > > > > > > diff --git a/drivers/media/pci/ivtv/ivtvfb.c b/drivers/media/pci/ivtv/ivtvfb.c > > > > > index 4cb365d..8b95eef 100644 > > > > > --- a/drivers/media/pci/ivtv/ivtvfb.c > > > > > +++ b/drivers/media/pci/ivtv/ivtvfb.c > > > > > @@ -38,6 +38,8 @@ > > > > > Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA > > > > > */ > > > > > > > > > > +#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt > > > > > + > > > > > #include > > > > > #include > > > > > #include > > > > > @@ -1171,6 +1173,13 @@ static int ivtvfb_init_card(struct ivtv *itv) > > > > > { > > > > > int rc; > > > > > > > > > > +#ifdef CONFIG_X86_64 > > > > > + if (pat_enabled()) { > > > > > + pr_warn("ivtvfb needs PAT disabled, boot with nopat kernel parameter\n"); > > > > > + return -ENODEV; > > > > > + } > > > > > +#endif > > > > > + > > > > > if (itv->osd_info) { > > > > > IVTVFB_ERR("Card %d already initialised\n", ivtvfb_card_id); > > > > > return -EBUSY; > > > > > > > > Same argument as for ipath: why not make arch_phys_wc_add() fail on PAT and > > > > return -1, and check it in arch_phys_wc_del()? > > > > > > The arch_phys_wc_add() is a no-op for PAT systems but for PAT to work we need > > > not only need to add this in where we replace the MTRR call but we also need to > > > convert ioremap_nocache() calls to ioremap_wc() but only if things were split up > > > already. > > > > Hi Ingo, > > > We don't need to do that: for such legacy drivers we can fall back to UC just > > fine, and inform the user that by booting with 'nopat' the old behavior will be > > back... > > This is really a "user experience" decision. > > IMO anyone who is still using ivtvfb and an old conventional PCI PVR-350 to > render, at SDTV resolution, an X Desktop display or video playback on a > television screen, isn't going to give a hoot about modern things like PAT. The > user will simply want the framebuffer performance they are accustomed to having > with their system. UC will probably yield unsatisfactory performance for an > ivtvfb framebuffer. > > With that in mind, I would think it better to obviously and clearly disable the > ivtvfb framebuffer module with PAT enabled, so the user will check the log and > read the steps needed to obtain acceptable performance. > > Maybe that's me just wanting to head off the "poor ivtvfb performance with > latest kernel" bug reports. > > Whatever the decision, my stock response to bug reports related to this will > always be "What do the logs say?". So what if that frame buffer is their only (working) frame buffer? A slow framebuffer is still much better at giving people logs to look at than a non-working one. Thanks, Ingo