On 8/12/2014 9:48 AM, Grant Likely wrote: > On Wed, 6 Aug 2014 17:02:44 -0500, Rob Herring <robherring2@xxxxxxxxx> wrote: >> On Wed, Aug 6, 2014 at 3:30 PM, Al Cooper <alcooperx@xxxxxxxxx> wrote: >>> __reserved_mem_reserve_reg() won't reserve memory if the base address >>> is zero. This change removes the check for a base address of zero and >>> allows it to be reserved. >>> >>> Allowing the first 4K of memory to be reserved will help solve a >>> problem on some ARM systems where the the first 16K of memory is >>> unused and becomes allocable memory. This will prevent this memory >>> from being used for DMA by drivers like the USB OHCI driver which >>> consider a physical address of zero to be illegal. >> >> OHCI driver or hardware? I agree with the change, but really think >> this should be fixed in the driver in the former case or a property of >> the OHCI node in the latter. > > I'm not hard and fast on that. I don't think it is unreasonable to > reserve the base of memory as the platform level if there is a bug > causing DMA to fail at that address. > > If this is a common problem (and not merely a few boards) then I agree. > Fixing it this way is just asking for the same problem to show up again > and again on new boards that haven't explicitly reserved the memory. > > g. > Reserving memory at physical address 0 has been semi-common on our boards for many issues. Sometimes it's been for temporary debugging purposes to catch an unknown driver corrupting physical address 0. Sometimes it has been a permanent fix to a hardware limitation. Thanks, Laura -- Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
