Re: [PATCH] soundwire: stream: fix programming slave ports for non-continous port maps

[Krzysztof Kozlowski]

On 30/07/2024 10:23, Krzysztof Kozlowski wrote:
> On 29/07/2024 16:25, Pierre-Louis Bossart wrote:
>>
>>
>> On 7/29/24 16:01, Krzysztof Kozlowski wrote:
>>> Two bitmasks in 'struct sdw_slave_prop' - 'source_ports' and
>>> 'sink_ports' - define which ports to program in
>>> sdw_program_slave_port_params().  The masks are used to get the
>>> appropriate data port properties ('struct sdw_get_slave_dpn_prop') from
>>> an array.
>>>
>>> Bitmasks can be non-continuous or can start from index different than 0,
>>> thus when looking for matching port property for given port, we must
>>> iterate over mask bits, not from 0 up to number of ports.
>>>
>>> This fixes allocation and programming slave ports, when a source or sink
>>> masks start from further index.
>>>
>>> Fixes: f8101c74aa54 ("soundwire: Add Master and Slave port programming")
>>> Cc: <stable@xxxxxxxxxxxxxxx>
>>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx>
>>
>> This is a valid change to optimize how the port are accessed.
>>
>> But the commit message is not completely clear, the allocation in
>> mipi_disco.c is not modified and I don't think there's anything that
>> would crash. If there are non-contiguous ports, we will still allocate
>> space that will not be initialized/used.
>>
>> 	/* Allocate memory for set bits in port lists */
>> 	nval = hweight32(prop->source_ports);
>> 	prop->src_dpn_prop = devm_kcalloc(&slave->dev, nval,
>> 					  sizeof(*prop->src_dpn_prop),
>> 					  GFP_KERNEL);
>> 	if (!prop->src_dpn_prop)
>> 		return -ENOMEM;
>>
>> 	/* Read dpn properties for source port(s) */
>> 	sdw_slave_read_dpn(slave, prop->src_dpn_prop, nval,
>> 			   prop->source_ports, "source");
>>
>> IOW, this is a valid change, but it's an optimization, not a fix in the
>> usual sense of 'kernel oops otherwise'.
>>
>> Am I missing something?
>>
>> BTW, the notion of DPn is that n > 0. DP0 is a special case with
>> different properties, BIT(0) cannot be set for either of the sink/source
>> port bitmask.
> 
> I think we speak about two different things. port num > 1, that's
> correct. But index for src_dpn_prop array is something different. Look
> at mipi-disco sdw_slave_read_dpn():
> 
> 173         u32 bit, i = 0;
> ...
> 178         addr = ports;
> 179         /* valid ports are 1 to 14 so apply mask */
> 180         addr &= GENMASK(14, 1);
> 181
> 182         for_each_set_bit(bit, &addr, 32) {
> ...
> 186                 dpn[i].num = bit;
> 
> 
> so dpn[0..i] = 1..n
> where i is also the bit in the mask.
> 
> Similar implementation was done in Qualcomm wsa and wcd codecs like:
> array indexed from 0:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/sound/soc/codecs/wcd938x-sdw.c?h=v6.11-rc1#n51
> 
> genmask from 0, with a mistake:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/sound/soc/codecs/wcd938x-sdw.c?h=v6.11-rc1#n1255
> 
> The mistake I corrected here:
> https://lore.kernel.org/all/20240726-asoc-wcd-wsa-swr-ports-genmask-v1-0-d4d7a8b56f05@xxxxxxxxxx/
> 
> To summarize, the mask does not denote port numbers (1...14) but indices
> of the dpn array which are from 0..whatever (usually -1 from port number).
> 

Let me also complete this with a real life example of my work in
progress. I want to use same dpn_prop array for sink and source ports
and use different masks. The code in progress is:

https://git.codelinaro.org/krzysztof.kozlowski/linux/-/commit/ef709a0e8ab2498751305367e945df18d7a05c78#6f965d7b74e712a5cfcbc1cca407b85443a66bac_2147_2157

Without this patch, I get -EINVAL from sdw_get_slave_dpn_prop():
  soundwire sdw-master-1-0: Program transport params failed: -22

Best regards,
Krzysztof