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

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Message-ID: <f5110f23-6d73-45b5-87a3-380bb70b9ac8@linaro.org>
Date: Tue, 3 Sep 2024 14:50:02 +0200
From: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To: "Liao, Bard" <yung-chuan.liao@...ux.intel.com>,
 Vinod Koul <vkoul@...nel.org>,
 Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc: Sanyog Kale <sanyog.r.kale@...el.com>, Shreyas NC <shreyas.nc@...el.com>,
 alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
 stable@...r.kernel.org, bard.liao@...el.com
Subject: Re: [PATCH] soundwire: stream: fix programming slave ports for
 non-continous port maps

On 03/09/2024 09:34, Liao, Bard wrote:
> 
> On 7/31/2024 2:56 PM, Vinod Koul wrote:
>> On 29-07-24, 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.
>> The fix seems right to me, we cannot have assumption that ports are
>> contagious, so we need to iterate over all valid ports and not to N
>> ports which code does now!
> 
> 
> Sorry to jump in after the commit was applied. But, it breaks my test.
> 
> The point is that dpn_prop[i].num where the i is the array index, and
> 
> num is the port number. So, `for (i = 0; i < num_ports; i++)` will iterate

Please fix your email client so it will write proper paragraphs.
Inserting blank lines after each sentence reduces the readability.

> 
> over all valid ports.
> 
> We can see in below drivers/soundwire/mipi_disco.c
> 
>          nval = hweight32(prop->sink_ports);
> 
>          prop->sink_dpn_prop = devm_kcalloc(&slave->dev, nval,
> 
> sizeof(*prop->sink_dpn_prop),
> 
>                                             GFP_KERNEL);
> 
> And sdw_slave_read_dpn() set data port properties one by one.
> 
> `for_each_set_bit(i, &mask, 32)` will break the system when port numbers

The entire point of the commit is to fix it for non-continuous masks.
And I tested it with non-continuous masks.

> 
> are not continuous. For example, a codec has source port number = 1 and 3,

Which codec? Can you give a link to exact line in *UPSTREAM* kernel.

> 
> then dpn_prop[0].num = 1 and dpn_prop[1].num = 3. And we need to go
> 
> throuth dpn_prop[0] and dpn_prop[1] instead of dpn_prop[1] and dpn_prop[3].
> 

What are the source or sink ports in your case? Maybe you just generate
wrong mask?

It's not only my patch which uses for_each_set_bit(). sysfs_slave_dpn
does the same.

Best regards,
Krzysztof