Hi Daniel, On 13/09/2018 16:55, Daniel Vetter wrote: > On Thu, Sep 13, 2018 at 04:26:53PM +0200, Neil Armstrong wrote: >> Hi Daniel, >> >> On 13/09/2018 15:21, Daniel Vetter wrote: >>> On Wed, Sep 12, 2018 at 01:06:07PM +0200, Noralf Trønnes wrote: >>>> >>>> Den 12.09.2018 12.57, skrev Noralf Trønnes: >>>>> (Cc: Daniel Vetter) >>>>> >>>> >>>> Somehow that CC was dropped somewhere after leaving email client. >>>> Trying once more. >>> >>> Yeah I just made myself unpopular. If you want SMEM_START, then you need >>> to carry a local patch now. virt_to_pfn on the vmap should work. It's >>> about 2 lines, including the change to drop HIDE_SMEM_START. >> >> Would it be totally unacceptable to add such 2 line : >> - enabled by a specific config depending on EXPERT and narrowed to specific platforms >> - printing a big fat pr_warning_once when used >> - with a big fat comment specifying when this code will be dropped and why we should not activate it > > module_param_debug auto-taints your kernel, I'd just go with that. Plus > CONFIG_EXPERT (or CONFIG_BROKEN). OK, I think you mean module_param_unsafe, but I see the point. > > But yes, I think that's something I'll happily ack. Must be acked by Dave > (and perhaps a few others too), since defacto this means we now suddenly > care about closed source blobs. I'd say get someone from amd and a few of > the driver maintainers on board with this (nouveau, Eric, Rob, Lucas, > ...), to make sure it really represents community consensus. I'll drop something, but I'm afraid a kernel won't have this hack, shouldn't this serie be delayed for a release ? @Noaralf, do you have a branch somewhere I can base a work on ? Neil > > Cheers, Daniel > >> >> Neil >>> >>> And if consensus is that hiding SMEM_START is not a nice idea, then I'm >>> sure we can reintroduce it through some slightly unpretty backdoor, even >>> with Noralf's generic code. So not really a good reason to reject the >>> cleanup I think. >>> -Daniel >>> >>> >>>>> Den 12.09.2018 11.56, skrev Maxime Ripard: >>>>>> On Wed, Sep 12, 2018 at 11:48:34AM +0200, Neil Armstrong wrote: >>>>>>> Hi Noralf, >>>>>>> >>>>>>> On 08/09/2018 15:46, Noralf Trønnes wrote: >>>>>>>> The CMA helper is already using the >>>>>>>> drm_fb_helper_generic_probe part of >>>>>>>> the generic fbdev emulation. This patch makes full use of the generic >>>>>>>> fbdev emulation by using its drm_client callbacks. This means that >>>>>>>> drm_mode_config_funcs->output_poll_changed and >>>>>>>> drm_driver->lastclose are >>>>>>>> now handled by the emulation code. Additionally fbdev >>>>>>>> unregister happens >>>>>>>> automatically on drm_dev_unregister(). >>>>>>>> >>>>>>>> The drm_fbdev_generic_setup() call is put after >>>>>>>> drm_dev_register() in the >>>>>>>> driver. This is done to highlight the fact that fbdev emulation is an >>>>>>>> internal client that makes use of the driver, it is not part of the >>>>>>>> driver as such. If fbdev setup fails, an error is printed, >>>>>>>> but the driver >>>>>>>> succeeds probing. >>>>>>> I can't really ack/nack this move, on one side it's great to have a >>>>>>> generic fbdev emulation instead of the old fbdev code, but on the >>>>>>> other side the Amlogic platform (like allwinner, samsung, rockchip, >>>>>>> ...) still relies on an Fbdev variant of the libMali that uses >>>>>>> smem_start... >>>>>>> >>>>>>> I know it's dirty and fbdev based code should be legacy now, but I >>>>>>> consider it like an user-space breakage... >>>>>>> >>>>>>> I'll be happy if ARM provided it's Mali vendors a Fbdev libMali that >>>>>>> could use FBINFO_HIDE_SMEM_START and allocate BO's from the DRM >>>>>>> driver, it won't be the case and it will never be the case until the >>>>>>> Lima projects finalizes. >>>>>>> >>>>>>> So for me it's a no-go until Lima lands upstream in Linux *and* Mesa. >>>>>> My feelings exactly. If the choice is between reducing the DRM driver >>>>>> by a couple of dozens of lines or keeping the mali working, I'll pick >>>>>> the latter, every single day. >>>>> >>>>> I don't know the reasoning for blocking smem_start other than what Daniel >>>>> wrote in these commit messages: >>>>> >>>>> da6c7707caf3736c1cf968606bd97c07e79625d4 >>>>> fbdev: Add FBINFO_HIDE_SMEM_START flag >>>>> >>>>> DRM drivers really, really, really don't want random userspace to >>>>> share buffer behind it's back, bypassing the dma-buf buffer sharing >>>>> machanism. For that reason we've ruthlessly rejected any IOCTL >>>>> exposing the physical address of any graphics buffer. >>>>> >>>>> Unfortunately fbdev comes with that built-in. We could just set >>>>> smem_start to 0, but that means we'd have to hand-roll our own fb_mmap >>>>> implementation. For good reasons many drivers do that, but >>>>> smem_start/length is still super convenient. >>>>> >>>>> Hence instead just stop the leak in the ioctl, to keep fb mmap working >>>>> as-is. A second patch will set this flag for all drm drivers. >>>>> >>>>> >>>>> 6be8f3bd2c78915a9f3a058a346ae93068d35c01 >>>>> drm/fb: Stop leaking physical address >>>>> >>>>> For buffer sharing, use dma-buf instead. We can't set smem_start to 0 >>>>> unconditionally since that's used by the fbdev mmap default >>>>> implementation. And we have plenty of userspace which would like to >>>>> keep that working. >>>>> >>>>> This might break legit userspace - if it does we need to look at a >>>>> case-by-cases basis how to handle that. Worst case I expect overrides >>>>> for only specific drivers, since anything remotely modern should be >>>>> using dma-buf/prime now (which is about 7 years old now for DRM >>>>> drivers). >>>>> >>>>> This issue was uncovered because Noralf's rework to implement a >>>>> generic fb_probe also implements it's own fb_mmap callback. Which >>>>> means smem_start didn't have to be set anymore, which blew up some >>>>> blob in userspace rather badly. >>>>> >>>>> >>>>> Noralf. >>>>> >>>>> _______________________________________________ >>>>> dri-devel mailing list >>>>> dri-devel@xxxxxxxxxxxxxxxxxxxxx >>>>> https://lists.freedesktop.org/mailman/listinfo/dri-devel >>>>> >>>> >>> >> > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
