On Thursday, 9 August 2018 16:10:35 MSK Thierry Reding wrote: > On Thu, Aug 09, 2018 at 03:53:03PM +0300, Dmitry Osipenko wrote: > > On Thursday, 9 August 2018 13:45:41 MSK Thierry Reding wrote: > > > On Fri, Aug 03, 2018 at 02:30:47PM +0300, Dmitry Osipenko wrote: > > > > On Friday, 3 August 2018 13:50:55 MSK Thierry Reding wrote: > > > > > On Wed, Aug 01, 2018 at 06:08:07PM +0300, Dmitry Osipenko wrote: > > > > > > From time to time new bugs are popping up, causing some host1x > > > > > > client > > > > > > to > > > > > > fail its initialization. Currently a single clients initialization > > > > > > failure > > > > > > causes whole host1x device registration to fail, as a result a > > > > > > single > > > > > > DRM > > > > > > sub-device initialization failure makes whole DRM initialization > > > > > > to > > > > > > fail. > > > > > > Let's ignore clients initialization failure, as a result display > > > > > > panel > > > > > > lights up even if some DRM clients (say GR2D or VIC) fail to > > > > > > initialize. > > > > > > > > > > > > Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx> > > > > > > --- > > > > > > > > > > > > drivers/gpu/host1x/bus.c | 18 +++++++----------- > > > > > > 1 file changed, 7 insertions(+), 11 deletions(-) > > > > > > > > > > This is actually done on purpose. I can't think of a case where we > > > > > would > > > > > actively like to keep a half-broken DRM device operational. The > > > > > errors > > > > > that you're talking about should only happen during development, > > > > > > > > [only in a perfect world] > > > > > > gr2d and VIC are fairly deterministic. What are the errors you are > > > seeing that cause initialization failure? > > > > Right now there are no specific errors. There is only a known trouble with > > the ARM_DMA_USE_IOMMU, but that causes to fail all of the clients. > > > > > Note that it is possible for > > > these devices to malfunction even if initialization succeeds. A failure > > > to initialize can only happen if there's something wrong in the device > > > tree, firmware is missing (in case of VIC) or a regression was > > > introduced in some subsystem that causes a failure (maybe deferred probe > > > or something similar). > > > > A missing firmware is an actual good example. Though can't VIC driver be > > changed to load firmware at the time of a its first use by userspace? It > > should be very annoying that kernel driver forces you to churn with > > initramfs. > No, that's not really how firmware loading works. There's no technical > barrier to doing it, but it'd be strange. If a device needs firmware to > work, it'd be unusual to make it available before you know that it can > be used. > > What if the firmware can't be loaded at the time of the first use? How > do you report that back to userspace? -ENOENT because the firmware file > can't be found? How is userspace to know that this is a problem with > firmware loading rather than some other error having to do with the VIC > command stream being broken, for example? You'll have to check kernels log if there is some kernel-related failure in any case for the detailed information. > Modifying the initramfs is only necessary if you have the module built- > in or the module in the initramfs. If the module is in a root > filesystem, simply put the firmware there as well and you should be > good. This is all very standard Linux behaviour, nothing new or exotic > there. Having display driver built-in usually more preferable, it's not fun if kernel can't get to FS mount stage. > > > > > and the > > > > > device not showing up is a pretty good indicator that something is > > > > > wrong > > > > > as opposed to everything booting normally and then getting some > > > > > cryptic > > > > > error at runtime because one of the clients didn't initialize. > > > > > > > > If machine doesn't have a serial port and it doesn't have ssh server > > > > running or network doesn't come up, you'll end up with a completely > > > > dysfunctional piece of hardware. Hence there is no chance for you to > > > > even > > > > check what is wrong. The argument about a cryptic error doesn't make > > > > much > > > > sense, you have to improve your runtime as well (and you'll get a > > > > error > > > > message in the kernels log). > > > > > > You make a good point here. I'm not aware of any devices we support in > > > the kernel that don't have a serial console, but that doesn't mean the > > > kernel could be used on an "unsupported" device that doesn't have one. > > > > AFAIK, enabling serial on AC100 require soldering iron. > > > > > > > From my perspective, all clients should always be operational in > > > > > whatever baseline version you use. If it isn't that's a bug that > > > > > should > > > > > be fixed. Ideally those bugs should get fixed before making it into > > > > > a > > > > > baseline version (mainline, linux-next, ...), so that this never > > > > > impacts > > > > > even developers, unless they break it themselves, in which case > > > > > refusing > > > > > to register the DRM device is a pretty good incentive to fix it. > > > > > > > > Sounds like you're assuming that only kernel developers are supposed > > > > to > > > > use > > > > Tegra, though at least (for now) for upstream it is kinda true. Of > > > > course > > > > that could be changed ;-) > > > > > > That's not at all what I'm saying. What I am saying is that we should > > > make it difficult for developers to break the kernel in a way that would > > > put users into a position that is difficult to get themselves out of. If > > > we refuse to register the complete DRM device in case some subdevice > > > fails to initialize we increase the chances of developers noticing and > > > fixing it. > > > > > > If all we do on failure is output an error message, it's very likely to > > > go unnoticed. Developers are likely to check specifically the > > > functionality that they're working on and ignore failures that they may > > > have caused in other parts of the code as a side-effect of their current > > > work. > > > > I can try to help with improving of your automated testing suite, if > > you'll > > make it accessible to the public. > > This has nothing to do with automated test suites. The problem with test > suites is that you can't force everyone to run them, so it's likely that > people would still miss it. > > The whole point of failing the whole thing is to force people to do the > right thing irrespective of any test suite or log or whatever. So if I > work on display and accidentally break VIC initialization, I'm now > forced to fix VIC initialization if I want to be able to test display. > > > > Perhaps a good middle ground would be to turn initialization failures > > > into WARN_ON() to increase the chances of them getting notified and then > > > continue on a best effort basis in the hopes of having enough > > > initialized to get a message to users. > > > > Good to me, I'll make v2. > > > > > Another alternative would be to > > > mark essential subdevices (such as the display controller) so that only > > > they will cause failure to register the whole DRM device. > > > > I don't think that making some subdevice more valuable than the others is > > a > > feasible approach, how you are going to differentiate what of the two > > display controllers is more important than the other. > > I wasn't talking about one display controller vs. another, but rather > about "optional" subdevices. For example, I'd consider gr2d, gr3d and > VIC as optional in that they aren't needed to get something on the > screen. Anything display related would be considered required to make > sure people get at least a working display, even if all optional sub- > devices fail. Well, from a users perspective, likely that display panel is more important than HDMI port. It doesn't sound good that display panel won't work because of an unrelated HDMI issue (and vice versa). -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
