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

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Message-ID: <22b20ad7-8a25-4cb2-a24e-d6841b219977@linaro.org>
Date: Tue, 30 Jul 2024 10:23:04 +0200
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
 Vinod Koul <vkoul@...nel.org>, Bard Liao <yung-chuan.liao@...ux.intel.com>,
 Sanyog Kale <sanyog.r.kale@...el.com>, Shreyas NC <shreyas.nc@...el.com>,
 alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Cc: stable@...r.kernel.org
Subject: Re: [PATCH] soundwire: stream: fix programming slave ports for
 non-continous port maps

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@...r.kernel.org>
>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
> 
> 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@linaro.org/

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).


Best regards,
Krzysztof