Hi, On Wed, Oct 23, 2013 at 10:42:42AM -0400, Matt Porter wrote: > On Tue, Oct 22, 2013 at 04:38:52PM -0500, Rob Herring wrote: > > On 10/22/2013 06:25 AM, Matt Porter wrote: > > > On Tue, Oct 22, 2013 at 12:48:29PM +0200, Matthijs Kooijman wrote: > > >> Hi Kishon, > > >> > > >> On Mon, Oct 21, 2013 at 02:57:26PM +0530, Kishon Vijay Abraham I wrote: > > >>> I think it makes sense to keep the data width property in the dwc2 node itself. > > >>> I mean it describes how the dwc2 IP is configured in that particular SoC (given > > >>> that it can be either <8> or <16>). > > >> If I'm reading the RT3052 datasheet correctly (GHWCFG4 register), the IP > > >> can be configured for 8, 16 or 8 _and_ 16. In the latter case, the "8 > > >> and 16 supported" would make sense as a property of dwc2 (though this > > >> value should be autodetectable through GHWCFG4), while the actual 8 or > > >> 16 supported by the PHY would make sense as property of a phy. > > > > > > There would be no value in adding a property for an already detectable > > > value to dwc2's binding. To be honest, it's pretty much useless > > > information due to the existence of the "8 and 16" option. > > > > > >> Note sure if this is really useful in practice as well, or if just > > >> setting the actual width to use on dwc2 makes more sense... > > > > > > The GHWCFG4 information itself is not useful in practice, as described > > > in the original thread: https://lkml.org/lkml/2013/10/10/477 > > > > > > It's certainly useful in practice to have this width property in either > > > the dwc2 or the phy binding. One can make a case for either. As I > > > mentioned in the original post, if we put it in the phy binding we'll be > > > updating the generic phy binding. We'll then need an api added into the > > > generic phy framework to fetch the width of a phy. > > > > > > Both cases are doable and trivial, we just need the canonical decision > > > from a DT maintainer as to where the property belongs. Given that they > > > are in ARM ksummit, I'm not expecting to hear anything right this > > > moment. :) > > > > The host can support both, so it is not a property of the host and is a > > property of the phy. It is no different than what mode a SPI slave > > requires or whether an i2c slave supports 8 or 10-bit addressing. Those > > examples are all 1 to many rather than 1 to 1 where it doesn't really > > matter, but the same logic applies. > > Makes good sense, thanks. > > In this case, given the PHY ownership of width, we can completely avoid > any DT properties. The generic phy compliant BCM Kona phy driver can > report via the generic phy framework that it is 8-bit wide. There's no > support for this type of thing now but it's pretty trivial to add. > > I went ahead and did a quick proof-of-concept that adds a free-form > phy attributes struct for the generic phy. Given that generic phys can > be for any transmission technology this could be filled with a jumble > unrelated and often unpopulated attributes over time. In any case, the > below patch allows the phy provider to choose to specify utmi_width and > a controller driver that cares can use phy_get_attrs() to fetch the > optional phy attributes and use the utmi_width field if applicable. > > Kishon: I'll start a separate thread to discuss what approach you'd like > to see in the generic phy framework to manage this. > > -Matt > > diff --git a/include/linux/phy/phy.h b/include/linux/phy/phy.h > index 6d72269..b763d7b 100644 > --- a/include/linux/phy/phy.h > +++ b/include/linux/phy/phy.h > @@ -38,6 +38,14 @@ struct phy_ops { > }; > > /** > + * struct phy_attrs - represents phy attributes > + * @utmi_width: Data path width implemented by UTMI PHY > + */ > +struct phy_attrs { > + int utmi_width; this is supposed to be a generic PHY layer and as such, it shouldn't know about USB details such as the UTMI bus. How about calling bus_width just to make it more generic ? Then it would work for UTMI, PIPE3, ULPI, SLPI (did that even fly ?) or any other PHY <-> link interconnect. -- balbi
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