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

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Message-ID: <095d7119-8221-450a-9616-2df6a0df4c77@linux.intel.com>
Date: Mon, 29 Jul 2024 16:25:28 +0200
From: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
 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 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.


> ---
>  drivers/soundwire/stream.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/soundwire/stream.c b/drivers/soundwire/stream.c
> index 7aa4900dcf31..f275143d7b18 100644
> --- a/drivers/soundwire/stream.c
> +++ b/drivers/soundwire/stream.c
> @@ -1291,18 +1291,18 @@ struct sdw_dpn_prop *sdw_get_slave_dpn_prop(struct sdw_slave *slave,
>  					    unsigned int port_num)
>  {
>  	struct sdw_dpn_prop *dpn_prop;
> -	u8 num_ports;
> +	unsigned long mask;
>  	int i;
>  
>  	if (direction == SDW_DATA_DIR_TX) {
> -		num_ports = hweight32(slave->prop.source_ports);
> +		mask = slave->prop.source_ports;
>  		dpn_prop = slave->prop.src_dpn_prop;
>  	} else {
> -		num_ports = hweight32(slave->prop.sink_ports);
> +		mask = slave->prop.sink_ports;
>  		dpn_prop = slave->prop.sink_dpn_prop;
>  	}
>  
> -	for (i = 0; i < num_ports; i++) {
> +	for_each_set_bit(i, &mask, 32) {
>  		if (dpn_prop[i].num == port_num)
>  			return &dpn_prop[i];
>  	}