From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <53F4B4DA.6050703@mitre.org> Date: Wed, 20 Aug 2014 10:46:50 -0400 From: Jeffrey Melville MIME-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit Subject: [Xenomai] rtdm_iomap_to_user caching followup List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: xenomai@xenomai.org All, There was a patch applied back in January 2013 to disable caching with memory areas mapped with rtdm_iomap_to_user. (http://www.xenomai.org/pipermail/xenomai/2013-January/027370.html) Henri Roosen followed up in September 2013 to say that he still saw caching behavior with rtdm_iomap_to_user. The original patch didn't cover the ifdef LINUX_VERSION_CODE >= KERNEL_VERSION(2,6,16) && defined(CONFIG_MMU). He submitted two patch options but I didn't see any responses. (http://www.xenomai.org/pipermail/xenomai/2013-September/029211.html) I'm currently working with a Zynq ZC706, using Xenomai 2.6.3 on top of the Xilinx fork of the 3.8 kernel, as described in the README. The FPGA guys gave me a test FPGA image with a (dumb) AXI slave that has a very small register space. Pulling a cache line actually overflows the register space and causes the bus to lock up. I added a logic analyzer block to the FPGA to confirm the access addresses. More importantly, I don't want any of that address space cached even when the register space gets bigger. I was able to fix my problems by changing this line: - remap_pfn_range(vma,from,(to) >> PAGE_SHIFT,size,prot); \ + remap_pfn_range(vma,from,(to) >> PAGE_SHIFT,size,pgprot_noncached(prot)); \ Can we apply the patch? I can provide a new one if it is lost. Or is there a better way to use rtdm_iomap_to_user that lets the caller specify caching behavior? I couldn't find one. As a side note, has anyone successfully used Xenomai with Zynq on kernels newer than 3.8? I haven't found any newer pre/post patches and haven't had time to play around with manually merging it yet. I'd be willing to help if this is an area of need. Cheers, Jeff