linux-kernel - Re: [PATCH 2/3] drivers: usb: dwc3: Add adjust_frame_length

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Date:	Mon, 27 Jul 2015 10:08:23 -0500
From:	Felipe Balbi <balbi@...com>
To:	Badola Nikhil <nikhil.badola@...escale.com>
CC:	"balbi@...com" <balbi@...com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 2/3] drivers: usb: dwc3: Add adjust_frame_length_quirk

On Mon, Jul 27, 2015 at 06:56:48AM +0000, Badola Nikhil wrote:
> > -----Original Message-----
> > From: Felipe Balbi [mailto:balbi@...com]
> > Sent: Thursday, July 23, 2015 8:39 PM
> > To: Felipe Balbi
> > Cc: Badola Nikhil-B46172; linux-kernel@...r.kernel.org; linux-
> > usb@...r.kernel.org; linux-omap@...r.kernel.org;
> > gregkh@...uxfoundation.org
> > Subject: Re: [PATCH 2/3] drivers: usb: dwc3: Add adjust_frame_length_quirk
> > 
> > Hi again,
> > 
> > On Thu, Jul 23, 2015 at 09:55:32AM -0500, Felipe Balbi wrote:
> > > > diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h index
> > > > 0447788..b7a5119 100644
> > > > --- a/drivers/usb/dwc3/core.h
> > > > +++ b/drivers/usb/dwc3/core.h
> > > > @@ -124,6 +124,7 @@
> > > >  #define DWC3_GEVNTCOUNT(n)	(0xc40c + (n * 0x10))
> > > >
> > > >  #define DWC3_GHWPARAMS8		0xc600
> > > > +#define DWC3_GFLADJ		0xc630
> > > >
> > > >  /* Device Registers */
> > > >  #define DWC3_DCFG		0xc700
> > > > @@ -234,6 +235,10 @@
> > > >  /* Global HWPARAMS6 Register */
> > > >  #define DWC3_GHWPARAMS6_EN_FPGA			(1 << 7)
> > > >
> > > > +/* Global Frame Length Adjustment Register */
> > > > +#define GFLADJ_30MHZ_REG_SEL		(1 << 7)
> > >
> > > always prepend with DWC3_ like *all* other macros in this file.
> > >
> > > Also, match docs to ease grepping. This should be called
> > > DWC3_GFLADJ_30MHZ_SDBND_SEL
> 
> GFLADJ_30MHZ_REG_SEL is the field's name in LS1021A Reference Manual
> as well as dwc3 databook. Though DWC3_GFLADJ_30MHZ_SDBND_SEL seems
> more relevant. 

databook calls it GFLADJ_30MHZ_SDBND_SEL, I checked before sending my
email.

> > yet another problem is that this register doesn't exist in *all* versions of
> > DWC3. It was introduced in version 2.50a so the branch I typed above needs
> > one extra check, and since it's getting so large, it deserves be factored out
> > into its own function.
> > 
> > static int dwc3_frame_length_adjustment(struct dwc3 *dwc, u32 fladj) {
> > 	u32 reg;
> > 	u32 dft;
> > 
> > 	if (dwc->revision <= DWC3_REVISION_250A)
> > 		return 0;
> > 
> > 	if (fladj == 0)
> > 		return 0;
> > 
> > 	reg = dwc3_readl(dwc->regs, DWC3_GFLADJ);
> > 	dft = reg & 0x3f; /* needs a mask macro */
> > 
> > 	if (!dev_WARN_ONCE(dwc->dev, dft == fladj,
> > 		"requested value same as default, ignoring\n")) {
> > 		reg &= ~0x3f; /* needs a mask macro */
> > 		reg |= DWC3_GFLADJ_30MHZ_SDBND_SEL |
> > 			DWC3_GFLADJ_30MHZ(fladj_value);
> > 
> > 		dwc3_writel(dwc->regs, DWC3_GFLADJ, reg);
> > 	}
> > }
> > 
> > you really *MUST* check this sort of this out when writing patches. It's not
> > only about *your* SoC. You gotta remember we have a ton of different
> > users and those a prone to major grumpyness should a completely unrelated
> > patch break their use case.
> > 
> > You have access to the IP's documentation, and that contains the entire
> > history of the IP itself, so it's easy to figure all of this out with a simple search
> > in the documentation.
> > 
> > One extra detail is that you were very careless when writing to the GFLADJ
> > register too. You simply wrote your 30MHz sideband value, potentially
> > clearing other bits which shouldn't be touched. That alone can add
> > regressions.
> > 
> > When resending, make sure all 3 patches reach linux-usb. I still can't find
> > patch 3/3.
> >
> 
> Will take care of above scenarios and resend patches cc'ing linux-usb
> in each of them.
> 
> Regarding acceptance of the patch only when it's used in glue layer,
> there is no freescale's glue layer present for dwc3 as of now.

if there is no glue layer, how are you testing your patch ?

> Furthermore, there is not any platform specific code required in glue
> layer apart from the ones present in dwc3/core.c. 

sorry ? core.c is generic for all users, the glue layer should somewhat
hide platform details such as clocks and PM. It's surprising if you
don't need anything on that side.

-- 
balbi

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