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

[Liao, Bard]

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];
> > >   	}