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It's observed that cpsw/cpdma is not working properly when CPPI descriptors are placed in DDR instead of internal CPPI RAM on am437x SoC: - rx/tx silently stops processing packets; - or - after boot it's working for sometime, but stuck once Network load is increased (ping is working, but iperf is not). (The same issue has not been reproduced on am335x and am57xx). It seems that write to HDP register processed faster by interconnect than writing of descriptor memory buffer in DDR, which is probably caused by store buffer / write buffer differences as these functions are implemented differently across devices. So, to fix this i come up with two minimal, required changes: 1) all accesses to the channel register HDP/CP/RXFREE registers should be done using sync IO accessors readl()/writel(), because all previous memory writes writes have to be completed before starting channel (write to HDP) or completing desc processing. 2) the change 1 only doesn't work on am437x and additional reading of desc's field is required right after the new descriptor was filled with data and before pointer on it will be stored in prev_desc->hw_next field or HDP register. In addition, to above changes this patch eliminates all relaxed ordering I/O accessors in this driver as suggested by David Miller to avoid such kind of issues in the future, but with one exception - relaxed IO accessors will still be used to fill desc in cpdma_chan_submit(), which is safe as there is read barrier at the end of write sequence, and because sync IO accessors usage here will affect on net performance. Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.