Fork of alistair23 Linux kernel for reMarkable from https://github.com/alistair23/linux
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The Switchtec hardware has two types of memory windows: LUTs and Direct. The first area in each BAR is for LUT windows and the remaining area is for the direct region. The total number of LUT entries is set by a configuration setting in hardware and they all must be the same size. (This is fixed by switchtec_ntb to be 64K.) switchtec_ntb enables the LUTs only for the first BAR and enables the highest power of two possible. Seeing the LUTs are at the beginning of the BAR, the direct memory window's alignment is affected. Therefore, the maximum direct memory window size can not be greater than the number of LUTs times 64K. The direct window in other BARs will not have this restriction as the LUTs will not be enabled there. LUTs will only be exposed through the NTB API if the use_lut_mw parameter is set. Seeing the Switchtec hardware, by default, configures BARs to be 4G a module parameter is given to limit the size of the advertised memory windows. Higher layers tend to allocate the maximum BAR size and this has a tendency to fail when they try to allocate 4GB of contiguous memory. Signed-off-by: Logan Gunthorpe <logang@deltatee.com> Reviewed-by: Stephen Bates <sbates@raithlin.com> Reviewed-by: Kurt Schwemmer <kurt.schwemmer@microsemi.com> Acked-by: Allen Hubbe <Allen.Hubbe@dell.com> Signed-off-by: Jon Mason <jdmason@kudzu.us> |
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README
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.