> Subject: Re: IMX8MM 4GiB boundary issue > > On Fri, Sep 25, 2020 at 8:05 AM Marek Vasut <ma...@denx.de> wrote: > > > > On 9/25/20 4:52 PM, Tim Harvey wrote: > > > Greetings, > > > > > > I'm working with an IMX8MM board that has 4GiB of DRAM. I've found > > > that in this configuration the MMC driver and FEC network driver > > > appear to have some issues with crossing the 4GiB address space. If > > > I tell U-Boot I have 3GiB everything is ok, but when I set it to > > > 4GiB I see the following: > > > > > > MMC: FSL_SDHC: 0, FSL_SDHC: 1, FSL_SDHC: 2 > > > Loading Environment from MMC... Error found for upper 32 bits Error > > > found for upper 32 bits Error found for upper 32 bits > > > *** Warning - No block device, using default environment > > > > > > In: serial > > > Out: serial > > > Err: serial > > > Net: DP83867 > > > Warning: ethernet@30be0000 (eth0) using random MAC address - > > > ea:22:3a:4d:8f:d5 > > > eth0: ethernet@30be0000 [PRIME] > > > Hit any key to stop autoboot: 0 > > > > > > On the FEC ethernet side I don't see any errors reported but ping's > > > fail with 4GiB DRAM. > > > > > > I suspect drivers have 32bit addressing issues as the base of mem > > > for IMX8MM is 1GiB so anything over 3GiB of DRAM runs you over the > > > 32bit boundary. > > > > > > Anyone run into this yet? > > > > I saw similar things on RCar3 with 32bit IPs and used bounce buffers > > to work around the 32bit limitations where applicable. > > > > > Marek, I noticed you are the maintainer for the technexion > > > pico-imx8mq which has support for 1, 2, 3, and 4 GiB DRAM. Did you > > > encounter such issues on the 4GiB variant? > > > > I dont have the 4 GiB variant. > > ah... that explains why you didn't see it. Note a patch I just sent > 'imx8m: fix cache setup for dynamic sdram size' that your board will need as > well in order to boot with 4GiB. > > > > > I can imagine that either the FEC/SDHCI is limited to 32bit addressing > > in hardware (the DMA can only operate on 32bit range due to it coming > > from 32bit systems), OR, the drivers need to be patched to support the > > 64bit addresses properly on 64bit SoCs and 64bit variants of the IPs > > I hadn't thought about the DMA boundary issue. I'll wait for NXP to weigh in > before I start digging through drivers. I wonder if there is a simple > workaround > to make sure U-Boot is running in lower DRAM? I'm not all that clear where > U-Boot gets allocated.
The IP only support 32bits DMA, you could let U-Boot only relocated to the end of 4GB memory address space using get_effective_memsize Regards, Peng. > > Tim
