Re: [PATCH 2/5] usb: gadget: s3c-hsotg: support configurable UTMI PHY width

[Felipe Balbi <balbi@ti.com>]

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Hi,

On Thu, Oct 10, 2013 at 06:14:19PM +0000, Paul Zimmerman wrote:
> > From: Felipe Balbi [mailto:balbi@ti.com]
> > Sent: Thursday, October 10, 2013 11:07 AM
> > 
> > On Thu, Oct 10, 2013 at 05:57:54PM +0000, Paul Zimmerman wrote:
> > > > From: Felipe Balbi [mailto:balbi@ti.com]
> > > > Sent: Thursday, October 10, 2013 10:46 AM
> > > >
> > > > On Thu, Oct 10, 2013 at 12:54:40PM -0400, Matt Porter wrote:
> > > > > On 10/10/2013 11:29 AM, Felipe Balbi wrote:
> > > > > >On Mon, Oct 07, 2013 at 06:12:29AM -0400, Matt Porter wrote:
> > > > > >>Extend dwc2 binding with an optional utmi phy width property.
> > > > > >>Enable the s3c-hsotg.c driver to use standard dwc2 binding
> > > > > >>and enable configuration of the UTMI phy width based on the
> > > > > >>property.
> > > > > >>
> > > > > >>Signed-off-by: Matt Porter <matt.porter@linaro.org>
> > > > > >>Reviewed-by: Markus Mayer <markus.mayer@linaro.org>
> > > > > >>Reviewed-by: Tim Kryger <tim.kryger@linaro.org>
> > > > > >>---
> > > > > >>  Documentation/devicetree/bindings/staging/dwc2.txt |  4 ++++
> > > > > >>  drivers/usb/gadget/s3c-hsotg.c                     | 18 +++++++++++++++++-
> > > > > >>  drivers/usb/gadget/s3c-hsotg.h                     |  1 +
> > > > > >>  3 files changed, 22 insertions(+), 1 deletion(-)
> > > > > >>
> > > > > >>diff --git a/Documentation/devicetree/bindings/staging/dwc2.txt
> > > > b/Documentation/devicetree/bindings/staging/dwc2.txt
> > > > > >>index 1a1b7cf..fb6b8ee 100644
> > > > > >>--- a/Documentation/devicetree/bindings/staging/dwc2.txt
> > > > > >>+++ b/Documentation/devicetree/bindings/staging/dwc2.txt
> > > > > >>@@ -6,10 +6,14 @@ Required properties:
> > > > > >>  - reg : Should contain 1 register range (address and length)
> > > > > >>  - interrupts : Should contain 1 interrupt
> > > > > >>
> > > > > >>+Optional properties:
> > > > > >>+- snps,phy-utmi-width: Must contain the UTMI data width (either 8 or 16)
> > > > > >
> > > > > >isn't this available in any of the configuration registers ?
> > > > >
> > > > > Yes and no. HWCFG4 has a UTMI data width field. However, it has 3
> > > > > valid states, "8", "16", or "8 or 16". The BCM281xx implementation is
> > > > > set to the latter and the attached phy is 8-bit.
> > > > >
> > > > > Looking at dwc2 prior to Matthijs Kooijman's patch [1] which starts
> > > > > validating the value of phy_utmi_width in that driver, the pci.c
> > > > > dwc2_module_params .phy_utmi_width field there even had the comment,
> > > > > "/* 16 bits - NOT DETECTABLE */". The autodetect code in
> > > > > dwc2_set_param_phy_utmi_width() will fail if HWCFG4 has the "8 or 16"
> > > > > option as it just decides to default to a phy width of 16 if nothing
> > > > > is configured by the platform glue. This property would also allow
> > > > > this issue to be addressed in that driver.
> > > >
> > > > fair enough, but I'd really like to hear from DT folks if your suggested
> > > > binding is acceptable. It seems like we can equally argue that it's a SW
> > > > configuration or HW description.
> > >
> > > It's definitely a HW description - the width of the UTMI data connection.
> > 
> > right, but that description should be passed to the PHY, right ? DWC2
> > works with both widths (8 or 16).
> 
> I don't know what you mean by "passed to the PHY". The data width is the
> number of physical wires connecting the PHY to the DWC2 controller. If

right, that's well understood.

> that value can be read from the PHY, fine. Otherwise, I think a DT
> binding is the way to go.

Let's see what the DT folks have to say.

-- 
balbi

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