[PATCH 2/3] drm/i915/gt: Document function to decode register state context

[Matt Roper]

On Thu, Sep 29, 2022 at 10:09:02PM -0700, Lucas De Marchi wrote:
> It's no obviously clear how the encode/decode of the per platform tables

This should probably say "...not obvious..." or "...not clear..."

Otherwise,

Reviewed-by: Matt Roper <matthew.d.roper at intel.com>

> 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 at intel.com>
> ---
>  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
> 

-- 
Matt Roper
Graphics Software Engineer
VTT-OSGC Platform Enablement
Intel Corporation