Re: [RFC PATCH 09/16] soundwire: crc8: add constant table

[Vinod Koul <vkoul@kernel.org>]

On 18-12-23, 14:26, Pierre-Louis Bossart wrote:
> 
> 
> On 12/18/23 06:01, Vinod Koul wrote:
> > On 07-12-23, 16:29, Pierre-Louis Bossart wrote:
> >> Add the lookup table required by crc8(). All configuration values were
> >> directly table from the MIPI SoundWire 1.x specification.
> >>
> >> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
> >> ---
> >>  drivers/soundwire/Makefile |   4 +-
> >>  drivers/soundwire/crc8.c   | 277 +++++++++++++++++++++++++++++++++++++
> >>  drivers/soundwire/crc8.h   |  11 ++
> >>  3 files changed, 291 insertions(+), 1 deletion(-)
> >>  create mode 100644 drivers/soundwire/crc8.c
> >>  create mode 100644 drivers/soundwire/crc8.h
> >>
> >> diff --git a/drivers/soundwire/Makefile b/drivers/soundwire/Makefile
> >> index 657f5888a77b..170128dd9318 100644
> >> --- a/drivers/soundwire/Makefile
> >> +++ b/drivers/soundwire/Makefile
> >> @@ -5,7 +5,9 @@
> >>  
> >>  #Bus Objs
> >>  soundwire-bus-y := bus_type.o bus.o master.o slave.o mipi_disco.o stream.o  \
> >> -			sysfs_slave.o sysfs_slave_dpn.o
> >> +			sysfs_slave.o sysfs_slave_dpn.o \
> >> +			crc8.o
> >> +
> >>  obj-$(CONFIG_SOUNDWIRE) += soundwire-bus.o
> >>  
> >>  soundwire-generic-allocation-objs := generic_bandwidth_allocation.o
> >> diff --git a/drivers/soundwire/crc8.c b/drivers/soundwire/crc8.c
> >> new file mode 100644
> >> index 000000000000..b6b984d7f39a
> >> --- /dev/null
> >> +++ b/drivers/soundwire/crc8.c
> >> @@ -0,0 +1,277 @@
> >> +// SPDX-License-Identifier: (GPL-2.0 OR BSD-3-Clause)
> >> +// Copyright(c) 2024 Intel Corporation.
> >> +
> >> +#include <linux/crc8.h>
> >> +#include <linux/module.h>
> >> +#include "crc8.h"
> >> +
> >> +/*
> >> + * the MIPI SoundWire CRC8 polynomial is X^8 + X^6 + X^3 + X^2 + 1, MSB first
> >> + * The value is (1)01001101 = 0x4D
> >> + *
> >> + * the table below was generated with
> >> + *
> >> + *	u8 crc8_lookup_table[CRC8_TABLE_SIZE];
> >> + *	crc8_populate_msb(crc8_lookup_table, SDW_CRC8_POLY);
> > 
> > Good that you found this API, so next question would be why should we
> > have this static table in kernel and not generate on probe if bpt is
> > supported..? Many subsystems use these APIs to generate the tables..
> 
> The table is going to be the same for all hosts, it's simpler if
> everyone uses a constant table, no? We're talking about 256 bytes added
> for the common bus parts, be it with dynamically allocated memory or a
> static table.
> 
> I don't mind reverting to a dynamically allocated table populated at
> boot if that was the consensus.

Most of the kernel users I looked have dynamically allocated table
populated at boot, also out of many users how many would support BTP.?
Your older platforms, current qcom dont, so not point is adding for
everyone...


-- 
~Vinod