Re: [alsa-devel] [RESEND PATCH v4 2/4] soundwire: core: add device tree support for slave devices

[Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>]

On 23/08/2019 16:44, Pierre-Louis Bossart wrote:
> On 8/22/19 6:37 PM, Srinivas Kandagatla wrote:
> > This patch adds support to parsing device tree based
> > SoundWire slave devices.
> >
> > Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> > ---
> >   drivers/soundwire/bus.c   |  2 ++
> >   drivers/soundwire/bus.h   |  1 +
> >   drivers/soundwire/slave.c | 52 +++++++++++++++++++++++++++++++++++++++
> >   3 files changed, 55 insertions(+)
> >
> > diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
> > index 49f64b2115b9..c2eaeb5c38ed 100644
> > --- a/drivers/soundwire/bus.c
> > +++ b/drivers/soundwire/bus.c
> > @@ -77,6 +77,8 @@ int sdw_add_bus_master(struct sdw_bus *bus)
> >        */
> >       if (IS_ENABLED(CONFIG_ACPI) && ACPI_HANDLE(bus->dev))
> >           ret = sdw_acpi_find_slaves(bus);
> > +    else if (IS_ENABLED(CONFIG_OF) && bus->dev->of_node)
> > +        ret = sdw_of_find_slaves(bus);
> >       else
> >           ret = -ENOTSUPP; /* No ACPI/DT so error out */
> > diff --git a/drivers/soundwire/bus.h b/drivers/soundwire/bus.h
> > index 3048ca153f22..ee46befedbd1 100644
> > --- a/drivers/soundwire/bus.h
> > +++ b/drivers/soundwire/bus.h
> > @@ -15,6 +15,7 @@ static inline int sdw_acpi_find_slaves(struct 
> > sdw_bus *bus)
> >   }
> >   #endif
> > +int sdw_of_find_slaves(struct sdw_bus *bus);
> >   void sdw_extract_slave_id(struct sdw_bus *bus,
> >                 u64 addr, struct sdw_slave_id *id);
> > diff --git a/drivers/soundwire/slave.c b/drivers/soundwire/slave.c
> > index f39a5815e25d..3ef265d2ee89 100644
> > --- a/drivers/soundwire/slave.c
> > +++ b/drivers/soundwire/slave.c
> > @@ -2,6 +2,7 @@
> >   // Copyright(c) 2015-17 Intel Corporation.
> >   #include <linux/acpi.h>
> > +#include <linux/of.h>
> >   #include <linux/soundwire/sdw.h>
> >   #include <linux/soundwire/sdw_type.h>
> >   #include "bus.h"
> > @@ -35,6 +36,7 @@ static int sdw_slave_add(struct sdw_bus *bus,
> >       slave->dev.release = sdw_slave_release;
> >       slave->dev.bus = &sdw_bus_type;
> > +    slave->dev.of_node = of_node_get(to_of_node(fwnode));
> >       slave->bus = bus;
> >       slave->status = SDW_SLAVE_UNATTACHED;
> >       slave->dev_num = 0;
> > @@ -112,3 +114,53 @@ int sdw_acpi_find_slaves(struct sdw_bus *bus)
> >   }
> >   #endif
> > +
> > +/*
> > + * sdw_of_find_slaves() - Find Slave devices in master device tree node
> > + * @bus: SDW bus instance
> > + *
> > + * Scans Master DT node for SDW child Slave devices and registers it.
> > + */
> > +int sdw_of_find_slaves(struct sdw_bus *bus)
> > +{
> > +    struct device *dev = bus->dev;
> > +    struct device_node *node;
> > +
> > +    for_each_child_of_node(bus->dev->of_node, node) {
> > +        int link_id, sdw_version, ret, len;
> > +        const char *compat = NULL;
> > +        struct sdw_slave_id id;
> > +        const __be32 *addr;
> > +
> > +        compat = of_get_property(node, "compatible", NULL);
> > +        if (!compat)
> > +            continue;
> > +
> > +        ret = sscanf(compat, "sdw%01x%04hx%04hx%02hhx", &sdw_version,
> > +                 &id.mfg_id, &id.part_id, &id.class_id);
> > +
> > +        if (ret != 4) {
> > +            dev_err(dev, "Invalid compatible string found %s\n",
> > +                compat);
> > +            continue;
> > +        }
> > +
> > +        addr = of_get_property(node, "reg", &len);
> > +        if (!addr || (len < 2 * sizeof(u32))) {
> > +            dev_err(dev, "Invalid Instance and Link ID\n");
> > +            continue;
> > +        }
> > +
> > +        id.unique_id = be32_to_cpup(addr++);
> > +        link_id = be32_to_cpup(addr);
>
> So here the link ID is obviously not in the address, so you are not 
> using the MIPI spec as we discussed initially?

No, Rob rejected that approach (https://lkml.org/lkml/2019/8/22/490) 
with the fact that compatible string should be constant for each instance.

--srini
> > +        id.sdw_version = sdw_version;
> > +
> > +        /* Check for link_id match */
> > +        if (link_id != bus->link_id)
> > +            continue;
> > +
> > +        sdw_slave_add(bus, &id, of_fwnode_handle(node));
> > +    }
> > +
> > +    return 0;
> > +}