On Tue, Mar 15, 2016 at 03:24:46PM +0000, Alexey Brodkin wrote:
> Hi Daniel,
>
> On Tue, 2016-03-15 at 09:10 +0100, Daniel Vetter wrote:
> > On Mon, Mar 14, 2016 at 11:15:59AM +0000, Alexey Brodkin wrote:
> > >
> > > On Mon, 2016-03-14 at 08:00 +0100, Daniel Vetter wrote:
> > > >
> > > > On Fri, Mar 11, 2016 at 06:42:36PM +0300, Alexey Brodkin wrote:
> > > > >
> > > > > +static int arcpgu_atomic_commit(struct drm_device *dev,
> > > > > + ????struct drm_atomic_state *state, bool async)
> > > > > +{
> > > > > + return drm_atomic_helper_commit(dev, state, false);
> > > > Note that this isn't really async if you ever get around to implement
> > > > fence support or vblank support. Just fyi.
> > > Ok but for now should I leave it as it is?
> > Yeah ok as-is, hence just fyi.
>
> Thanks. Just wanted to make sure we're on the same page :)
>
> > >
> > > >
> > > > >
> > > > > +static struct drm_driver arcpgu_drm_driver = {
> > > > > + .driver_features = DRIVER_MODESET | DRIVER_GEM | DRIVER_PRIME |
> > > > > + ???DRIVER_ATOMIC,
> > > > > + .preclose = arcpgu_preclose,
> > > > > + .lastclose = arcpgu_lastclose,
> > > > > + .name = "drm-arcpgu",
> > > > > + .desc = "ARC PGU Controller",
> > > > > + .date = "20160219",
> > > > > + .major = 1,
> > > > > + .minor = 0,
> > > > > + .patchlevel = 0,
> > > > > + .fops = &arcpgu_drm_ops,
> > > > > + .load = arcpgu_load,
> > > > > + .unload = arcpgu_unload,
> > > > Load and unload hooks are deprecated (it's a classic midlayer mistake).
> > > > Please use drm_dev_alloc/register pairs directly instead, and put your
> > > > device setup code in-between. Similar for unloading. There's a bunch of
> > > > example drivers converted already.
> > > Ok I took "atmel-hlcdc" as example.
> > > And that's interesting.
> > >
> > > If I put my?arcpgu_load() in between?drm_dev_alloc() and
> > > drm_dev_register() then I'm getting this on the driver probe:
> > > ---------------------------------->8-------------------------------
> > > [drm] Initialized drm 1.1.0 20060810
> > > arcpgu e0017000.pgu: arc_pgu ID: 0xabbabaab
> > > ------------[ cut here ]------------
> > > WARNING: CPU: 0 PID: 1 at lib/kobject.c:244 kobject_add_internal+0x17c/0x498()
> > > kobject_add_internal failed for card0-HDMI-A-1 (error: -2 parent: card0)
> > > Modules linked in:
> > > CPU: 0 PID: 1 Comm: swapper Not tainted 4.5.0-rc3-01062-ga447822-dirty #17
> > >
> > > Stack Trace:
> > > ? arc_unwind_core.constprop.1+0xa4/0x110
> > > ? warn_slowpath_fmt+0x6e/0xfc
> > > ? kobject_add_internal+0x17c/0x498
> > > ? kobject_add+0x98/0xe4
> > > ? device_add+0xc6/0x734
> > > ? device_create_with_groups+0x12a/0x144
> > > ? drm_sysfs_connector_add+0x54/0xe8
> > > ? arcpgu_drm_hdmi_init+0xd4/0x17c
> > > ? arcpgu_probe+0x138/0x24c
> > > ? platform_drv_probe+0x2e/0x6c
> > > ? really_probe+0x212/0x35c
> > > ? __driver_attach+0x90/0x94
> > > ? bus_for_each_dev+0x46/0x80
> > > ? bus_add_driver+0x14e/0x1b4
> > > ? driver_register+0x64/0x108
> > > ? do_one_initcall+0x86/0x194
> > > ? kernel_init_freeable+0xf0/0x188
> > > ---[ end trace c67166ad43ddcce2 ]---
> > > [drm:drm_sysfs_connector_add] adding "HDMI-A-1" to sysfs
> > > [drm:drm_sysfs_connector_add] *ERROR* failed to register connector device: -2
> > > arcpgu e0017000.pgu: failed to regiter DRM connector and helper funcs
> > > arcpgu: probe of e0017000.pgu failed with error -2
> > > ---------------------------------->8-------------------------------
> > >
> > > But if I move arcpgu_load() after drm_dev_register() then everything
> > > starts properly and I may see HDMI screen works perfectly fine.
> > >
> > > Any thoughts?
> > Oops, yeah missed that detail. If you look at atmel it has a loop to
> > register all the drm connectors _after_ calling drm_dev_register().
> > Totally forgot about that. Can you pls
> > - Extract a new drm_connector_register_all() function
> > ? (atmel_hlcdc_dc_connector_plug_all seems to be the best template),
> > ? including kerneldoc.
> > - Adjust kerneldoc of drm_dev_register() to mention
> > ? drm_connector_register_all() and that ordering constraint.
> > - Roll that helper out to all the drivers that currently hand-roll it (one
> > ? patch per driver).
> >
> > I know a bit of work but imo not too much, and by doing some small
> > refactoring every time someone stumbles over a drm pitfall we keep the
> > subsystem clean&easy to understand. You're up for this? Would be a prep
> > series, I'll happily review it to get it merged fast. Just a few weeks ago
> > I merged 20+ patches to make ->mode_fixup hooks optional and remove dummy
> > ones all over the subsystem, in other words: You'll have my full attention
> > ;-)
>
> Sure, I'm ready to pay that price :)
> Stay tuned and patches will follow.
Awesome, looking forward to your patches.
> > >
> > > >
> > > > >
> > > > > + .dumb_create = drm_gem_cma_dumb_create,
> > > > > + .dumb_map_offset = drm_gem_cma_dumb_map_offset,
> > > > > + .dumb_destroy = drm_gem_dumb_destroy,
> > > > > + .get_vblank_counter = drm_vblank_no_hw_counter,
> > > > > + .prime_handle_to_fd = drm_gem_prime_handle_to_fd,
> > > > > + .prime_fd_to_handle = drm_gem_prime_fd_to_handle,
> > > > > + .gem_free_object = drm_gem_cma_free_object,
> > > > > + .gem_vm_ops = &drm_gem_cma_vm_ops,
> > > > > + .gem_prime_export = drm_gem_prime_export,
> > > > > + .gem_prime_import = drm_gem_prime_import,
> > > > > + .gem_prime_get_sg_table = drm_gem_cma_prime_get_sg_table,
> > > > > + .gem_prime_import_sg_table = drm_gem_cma_prime_import_sg_table,
> > > > > + .gem_prime_vmap = drm_gem_cma_prime_vmap,
> > > > > + .gem_prime_vunmap = drm_gem_cma_prime_vunmap,
> > > > > + .gem_prime_mmap = drm_gem_cma_prime_mmap,
> > > > > +};
> > > > > +
> > > > > +static int arcpgu_probe(struct platform_device *pdev)
> > > > > +{
> > > > > + return drm_platform_init(&arcpgu_drm_driver, pdev);
> > > > ... or read the kerneldoc of this function, which also explains what you
> > > > should do ;-)
> > > Could you please point me to the relevant document?
> > > I wasn't able to find anything related from the first glance :(
> > The kerneldoc comment for drm_platform_init says it's deprecated, please
> > use drm_dev_alloc/register instead.
>
> Yeah I saw this. I was a bit confused with word "kerneldoc" thinking about
> .txt files in Documentation folder.
kerneldoc is the kernel-specific tool to parse the specially formatted
in-source comments starting with /**. Run
$ make htmldocs
and you should have the generated gpu docs in Documentation/DocBook/gpu/
which pulls all those together into something somewhat coherent.
>
> > >
> > > >
> > > > >
> > > > > +
> > > > > +/*
> > > > > + * This function is the only reason to have a copy of drm_fbdev_cma_init()
> > > > > + * here in this driver.
> > > > > + *
> > > > > + * In its turn this mmap() is required to mark user-space page as non-cached
> > > > > + * because it is just a mirror or real hardware frame-buffer.
> > > > > + */
> > > > > +static int arcpgu_mmap(struct fb_info *info, struct vm_area_struct *vma)
> > > > > +{
> > > > > + vma->vm_page_prot = pgprot_noncached(vma->vm_page_prot);
> > > > > + return vm_iomap_memory(vma, info->fix.smem_start, info->fix.smem_len);
> > > > > +}
> > > > This looks very fishy, no other drm driver even bothers with providing an
> > > > fb_mmap hook. What exactly do you need this for? Assuming you've mmapped
> > > > your fbcon drm_framebuffer correctly for kernel access things should just
> > > > work ...
> > > Indeed for kernel there's non need to that hack. Kernel deals directly with HW
> > > frame-buffer area (that address we get from gem->paddr). And so every byte written gets
> > > picked up by PGU and is then rendered on the display.
> > >
> > > But when user-space opens /dev/fb0 and mmaps() it deals with memory pages which
> > > are by default (at least on ARC) marked as "cached". I.e. user-space application
> > > (I use that nice demo app?https://github.com/qtproject/qt/blob/4.8/examples/qws/framebuffer/main.c)
> > > deals with frame-buffer via data cache. And that has 2 problems:
> > > ?[1] Since no explicit cache flush gets executed some data is left in data cache,
> > > ? ? ?i.e. some parts of the picture never reaches real PGU.
> > > ? ? ?See what happens on display -?http://imgur.com/iAbnnx3
> > > ? ? ?Those missing lines are exactly those 32-byte missing cache lines.
> > > ?[2] Even if we manage to flush data somehow massive amount of data that goes
> > > ? ? ?through data cache (let's sat 1080p at 30Hz) will thrash it and as a result
> > > ? ? ?there will be no benefit for other cache users to use cache.
> > >
> > > So we fix it simply marking pages mapped to user-space apps as uncached
> > > that effectively routes all FB data directly to memry instead of polluting cache.
> > >
> > > Hopefully that explanation makes sense.
> > Still strange that you're the only one who needs this. I think best case
> > would be to provide some mmap helpers for fbdev which remap to dumb buffer
> > helpers or something similar. That way other drivers don't need to.
>
> Ok I took another look and now see what's missing.
> All other arches implement their own?fb_pgprotect() in arch/X/include/asm/fb.h
> which does exactly what I need. So entire arcpgu_fbdev.c will be dumped in v4 :)
Ah, excellent.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
