On Tue, Mar 8, 2011 at 10:31 PM, Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > Hi David, > > On Monday 07 March 2011 22:35:31 David Cohen wrote: >> On Mon, Mar 7, 2011 at 11:19 PM, Laurent Pinchart wrote: >> > On Monday 07 March 2011 20:41:21 David Cohen wrote: >> >> On Mon, Mar 7, 2011 at 9:25 PM, Guzman Lugo, Fernando wrote: >> >> > On Mon, Mar 7, 2011 at 1:19 PM, David Cohen wrote: >> >> >> On Mon, Mar 7, 2011 at 9:17 PM, Guzman Lugo, Fernando wrote: >> >> >>> On Mon, Mar 7, 2011 at 7:10 AM, Michael Jones wrote: >> >> >>>> From e7dbe4c4b64eb114f9b0804d6af3a3ca0e78acc8 Mon Sep 17 00:00:00 >> >> >>>> 2001 From: Michael Jones <michael.jones@xxxxxxxxxxxxxxxx> >> >> >>>> Date: Mon, 7 Mar 2011 13:36:15 +0100 >> >> >>>> Subject: [PATCH] omap: iommu: disallow mapping NULL address >> >> >>>> >> >> >>>> commit c7f4ab26e3bcdaeb3e19ec658e3ad9092f1a6ceb allowed mapping >> >> >>>> the NULL address if da_start==0. ÂForce da_start to exclude the >> >> >>>> first page. >> >> >>> >> >> >>> what about devices that uses page 0? ipu after reset always starts >> >> >>> from 0x00000000 how could we map that address?? >> >> >> >> >> >> from 0x0? The driver sees da == 0 as error. May I ask you why do you >> >> >> want it? >> >> > >> >> > unlike DSP that you can load a register with the addres the DSP will >> >> > boot, IPU core always starts from address 0x00000000, so if you take >> >> > IPU out of reset it will try to access address 0x0 if not map it, >> >> > there will be a mmu fault. >> >> >> >> Hm. Looks like the iommu should not restrict any da. The valid da >> >> range should rely only on pdata. >> >> Michael, what about just update ISP's da_start on omap-iommu.c file? >> >> Set it to 0x1000. >> > >> > What about patching the OMAP3 ISP driver to use a non-zero value (maybe >> > -1) as an invalid/freed pointer ? >> >> I wouldn't be comfortable to use 0 (or NULL) value as valid address on >> ISP driver. > > Why not ? The IOMMUs can use 0x00000000 as a valid address. Whether we allow > it or not is a software architecture decision, not influenced by the IOMMU > hardware. As some peripherals (namely IPU) require mapping memory to > 0x00000000, the IOMMU layer must support it and not treat 0x00000000 > specially. All da == 0 checks to aim at catching invalid address values must > be removed, both from the IOMMU API and the IOMMU internals. Yes, it can use and IOMMU should not treat is specially. That's the aim of my patch: [PATCH v2 3/3] omap: iovmm: don't check 'da' to set IOVMF_DA_FIXED flag I'm not advocating to not allow 0x0, but to not use it when user is not requesting fixed da. In many sw architecture decisions 0x0 address is a special case. To avoid any misuse, IOMMU will not use it unless it's requested. If user is not requesting fixed 'da', it's not a problem to not give 0x0 anyway. IMO that's the safer option for all cases. > >> The 'da' range (da_start and da_end) is defined per VM and specified as >> platform data. IMO, to set da_start = 0x1000 seems to be> a correct approach >> for ISP as it's the only client for its IOMMU instance. > > We can do that, and then use 0 as an invalid pointer in the ISP driver. As the > IOMMU API will use another value (what about 0xffffffff, as for the userspace > mmap() call ?) to mean "invalid pointer", it might be better to use the same > value in the ISP driver. That can be done, of course. But the main point is in OMAP3 ISP all initial register values to read/write from/to memory are 0x0. It means sometimes we can catch bugs more easily by not mapping that address. So, IMO, OMAP3 ISP should not allow to map first page. But that's a special case for this driver only. Br, David > > -- > Regards, > > Laurent Pinchart > -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
