Dear Intel graphics folks, Am Freitag, den 30.05.2014, 13:45 +0200 schrieb Paul Menzel: > since commit 17fec8a0 [1] > > drm/i915: Use Graphics Base of Stolen Memory on all gen3+ > > Linux reads the register BSM (Base of Stolen Memory) directly to get the > base address of graphics stolen memory. With coreboot [2] and native > graphics init – note that everything works with the proprietary VGA > BIOS/Option ROM – this causes a regression [3] as this register is not > programmed at all. > > From the datasheet *Mobile Intel® 945 Express Chipset Family* [4] the > register BSM is described on page 290. > > Graphics Stolen Memory and TSEG are within DRAM space defined > under TOLUD. From the top of low used DRAM, (G)MCH claims 1 to > 64 MBs of DRAM for internal graphics if enabled. > > This register contains bits 31 to 20 of the base address of > stolen > DRAM memory. The host interface determines the base of > graphics stolen memory by subtracting the graphics stolen > memory size from TOLUD. See Device 0 TOLUD for more > explanations. > > Also see Figure 12 *Main Memory Address Range* in section 9.2 on page > 325. > > Unfortunately I am unable to find out how the graphics stolen memory > size is determined. I’d have thought it is used for the framebuffer, but > according to page 93 (Graphics Mode select (GMS)) that the framebuffer > size can only be 1 MB or 8 MB, which contradicts that it can be up to 64 > MB. > > If it is determined implicitly by the value I set the BSM to, where can > I find the recommendations what size to use? I’d guess it is dependent > on the RAM size, that means dependent if the system has 512 MB or 4 GB > for example. The datasheet documents the bits of the register BSM as Read Only (RO). So I am even more confused now. Thanks, Paul > [1] https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=17fec8a08698bcab98788e1e89f5b8e7502ababd > [2] http://www.coreboot.org/ > [3] https://bugs.freedesktop.org/show_bug.cgi?id=79038 > [4] http://www.intel.com/content/dam/www/public/us/en/documents/datasheets/mobile-945-express-chipset-datasheet.pdf > Document Number: 309219-006
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