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

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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@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.
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

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

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

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].




---
  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];
  	}



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