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

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Message-ID: <ZqngD56bXkx6vGma@matsya>
Date: Wed, 31 Jul 2024 12:26:15 +0530
From: Vinod Koul <vkoul@...nel.org>
To: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
Cc: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.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, stable@...r.kernel.org
Subject: Re: [PATCH] soundwire: stream: fix programming slave ports for
 non-continous port maps

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!

> 
> 
> > ---
> >  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];
> >  	}

-- 
~Vinod