It's no obviously clear how the encode/decode of the per platform tables is done. Document it so while adding tables for new platforms people can be confident they right things is being done. Signed-off-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx> --- drivers/gpu/drm/i915/gt/intel_lrc.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c index 3515882a91fb..7771a19008c6 100644 --- a/drivers/gpu/drm/i915/gt/intel_lrc.c +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c @@ -20,6 +20,30 @@ #include "intel_ring.h" #include "shmem_utils.h" +/* + * The per-platform tables are u8-encoded in @data. Decode @data and set the + * addresses' offset and commands in @regs. The following encoding is used + * for each byte. There are 2 steps: decoding commands and decoding addresses. + * + * Commands: + * [7]: create NOPs - number of NOPs are set in lower bits + * [6]: When creating MI_LOAD_REGISTER_IMM command, allow to set + * MI_LRI_FORCE_POSTED + * [5:0]: Number of NOPs or registers to set values to in case of + * MI_LOAD_REGISTER_IMM + * + * Addresses: these are decoded after a MI_LOAD_REGISTER_IMM command by "count" + * number of registers. They are set by using the REG/REG16 macros: the former + * is used for offsets smaller than 0x200 while the latter is for values bigger + * than that. Those macros already set all the bits documented below correctly: + * + * [7]: When a register offset needs more than 6 bits, use additional bytes, to + * follow, for the lower bits + * [6:0]: Register offset, without considering the engine base. + * + * This function only tweaks the commands and register offsets. Values are not + * filled out. + */ static void set_offsets(u32 *regs, const u8 *data, const struct intel_engine_cs *engine, -- 2.37.3
