On Wed, 2018-04-11 at 02:16 +0000, YC Chen wrote: > Hi Ben, > Thanks for your reply. You need to open password register before > modify extended CRT registers. Extended CRT registers cannot be > modified if the read back value of password register is 0. > Allow me to describe this issue more. This issue only happen on Intel > x86/x86_64 system actually. We found there is a another thread still > access VGA cursor registers when loading "ast" drm driver. VGA > register is index I/O register, if two threads access it alternately, > it may cause the un-expected settings. "ast" drm driver is using > related IO or MMIO to access register, and the thread is using > standard VGA IO(0x3d4) to access cursor register, so our solution is > disabling standard VGA decoding(Set VGACRA1 D to 1) at the entry > of "ast" driver load to avoid this issue.
Thanks. Pending testing on our systems to make sure it doesn't break anything (it shouldn't .. hopefully) Reviewed-by: Benjamin Herrenschmidt <b...@kernel.crashing.org> > Regards, > > Y.C. Chen > > -----Original Message----- > From: Benjamin Herrenschmidt [mailto:b...@kernel.crashing.org] > Sent: Wednesday, April 11, 2018 9:54 AM > To: YC Chen <yc_c...@aspeedtech.com>; email@example.com > Cc: airl...@redhat.com; e...@suse.com > Subject: Re: [PATCH] drm/ast: Fixed reboot test may cause system > hanged > > On Wed, 2018-04-11 at 09:27 +0800, Y.C. Chen wrote: > > index dac3558..82a2687 100644 > > --- a/drivers/gpu/drm/ast/ast_main.c > > +++ b/drivers/gpu/drm/ast/ast_main.c > > @@ -131,8 +131,8 @@ static int ast_detect_chip(struct drm_device > > *dev, > > bool *need_post) > > > > > > /* Enable extended register access */ > > - ast_enable_mmio(dev); > > ast_open_key(ast); > > + ast_enable_mmio(dev); > > Why that change ? The documentation doesn't really specify what the > "password" register is about. What does it "open" ? > > I'm being a bit paranoid because we had issues with earlier drivers > (before some of the latest changes to that code) where occasionally > on boot, the chip wouldn't respond to an MMIO to one of the VGA > registers, causing an EEH error which crashes on boot. > > So I want to make sure I understand what the changes precisely do. > > Cheers, > Ben. _______________________________________________ dri-devel mailing list firstname.lastname@example.org https://lists.freedesktop.org/mailman/listinfo/dri-devel