On Tue, 23 Jul 2013, Tomasz Figa wrote:
> On Tuesday 23 of July 2013 09:29:32 Tomasz Figa wrote:
> > Hi Alan,
Thanks for helping to clarify the issues here.
> > > Okay. Are PHYs _always_ platform devices?
> >
> > They can be i2c, spi or any other device types as well.
In those other cases, presumably there is no platform data associated
with the PHY since it isn't a platform device. Then how does the
kernel know which controller is attached to the PHY? Is this spelled
out in platform data associated with the PHY's i2c/spi/whatever parent?
> > > > > PHY. Currently this information is represented by name or
> ID
> > > > > strings embedded in platform data.
> > > >
> > > > right. It's embedded in the platform data of the controller.
> > >
> > > It must also be embedded in the PHY's platform data somehow.
> > > Otherwise, how would the kernel know which PHY to use?
> >
> > By using a PHY lookup as Stephen and I suggested in our previous
> > replies. Without any extra data in platform data. (I have even posted a
> > code example.)
I don't understand, because I don't know what "a PHY lookup" does.
> > > In this case, it doesn't matter where the platform_device structures
> > > are created or where the driver source code is. Let's take a simple
> > > example. Suppose the system design includes a PHY named "foo". Then
> > > the board file could contain:
> > >
> > > struct phy_info { ... } phy_foo;
> > > EXPORT_SYMBOL_GPL(phy_foo);
> > >
> > > and a header file would contain:
> > >
> > > extern struct phy_info phy_foo;
> > >
> > > The PHY supplier could then call phy_create(&phy_foo), and the PHY
> > > client could call phy_find(&phy_foo). Or something like that; make up
> > > your own structure tags and function names.
> > >
> > > It's still possible to have conflicts, but now two PHYs with the same
> > > name (or a misspelled name somewhere) will cause an error at link
> > > time.
> >
> > This is incorrect, sorry. First of all it's a layering violation - you
> > export random driver-specific symbols from one driver to another. Then
No, that's not what I said. Neither the PHY driver nor the controller
driver exports anything to the other. Instead, both drivers use data
exported by the board file.
> > imagine 4 SoCs - A, B, C, D. There are two PHY types PHY1 and PHY2 and
> > there are two types of consumer drivers (e.g. USB host controllers). Now
> > consider following mapping:
> >
> > SoC PHY consumer
> > A PHY1 HOST1
> > B PHY1 HOST2
> > C PHY2 HOST1
> > D PHY2 HOST2
> >
> > So we have to be able to use any of the PHYs with any of the host
> > drivers. This means you would have to export symbol with the same name
> > from both PHY drivers, which obviously would not work in this case,
> > because having both drivers enabled (in a multiplatform aware
> > configuration) would lead to linking conflict.
You're right; the scheme was too simple. Instead, the board file must
export two types of data structures, one for PHYs and one for
controllers. Like this:
struct phy_info {
/* Info for the controller attached to this PHY */
struct controller_info *hinfo;
};
struct controller_info {
/* Info for the PHY which this controller is attached to */
struct phy_info *pinfo;
};
The board file for SoC A would contain:
struct phy_info phy1 = {&host1);
EXPORT_SYMBOL(phy1);
struct controller_info host1 = {&phy1};
EXPORT_SYMBOL(host1);
The board file for SoC B would contain:
struct phy_info phy1 = {&host2);
EXPORT_SYMBOL(phy1);
struct controller_info host2 = {&phy1};
EXPORT_SYMBOL(host2);
And so on. This explicitly gives the connection between PHYs and
controllers. The PHY providers would use &phy1 or &phy2, and the PHY
consumers would use &host1 or &host2.
Alan Stern
--
To unsubscribe from this list: send the line "unsubscribe linux-doc" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
