linux-kernel - RE: [PATCH v3] USB: ehci-pci: USB host controller support for Intel Quark X1000

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Date:	Tue, 1 Jul 2014 01:50:05 +0000
From:	"Chen, Alvin" <alvin.chen@...el.com>
To:	Alan Stern <stern@...land.harvard.edu>
CC:	Jingoo Han <jg1.han@...sung.com>,
	David Laight <David.Laight@...LAB.COM>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"Ong, Boon Leong" <boon.leong.ong@...el.com>
Subject: RE: [PATCH v3] USB: ehci-pci: USB host controller support for Intel
 Quark X1000

> >
> > /*--------------------------------------------------------------------
> > -----*/
> > +#define PCI_DEVICE_ID_INTEL_QUARK_X1000_SOC		0x0939
> > +static inline bool is_intel_quark_x1000(struct pci_dev *pdev) {
> > +	return pdev->vendor == PCI_VENDOR_ID_INTEL &&
> > +		pdev->device == PCI_DEVICE_ID_INTEL_QUARK_X1000_SOC;
> > +}
> 
> Whether to put this test directly into ehci_pci_reset() or leave it as a separate
> subroutine is up to you.  I don't care either way.
I will just keep it.

> > +
> > +/*
> > +	* The offset of in/out threshold register is 0x84.
> > +	* And it is the register of 'hostpc'
> > +	* in memory-mapped EHCI controller.
> > +*/
> 
> 0x84 is the same as offset of the hostpc register in the Intel Moorestown
> controller.  hostpc is not present in general EHCI controllers.
>
OK, I will improve the comments.

> > +#define	intel_quark_x1000_insnreg01	hostpc
> > +
> > +/* The maximal ehci packet buffer size is 512 bytes */
> > +#define INTEL_QUARK_X1000_EHCI_MAX_PACKET_BUFFER_SIZE	512
> > +
> > +/* The threshold value set the register is in DWORD */
> > +#define INTEL_QUARK_X1000_EHCI_THRESHOLD(size)	((size)/4u)
> > +#define INTEL_QUARK_X1000_EHCI_THRESHOLD_OUT_SHIFT	16
> > +#define INTEL_QUARK_X1000_EHCI_THRESHOLD_IN_SHIFT	0
> > +
> >  /* called after powerup, by probe or system-pm "wakeup" */  static
> > int ehci_pci_reinit(struct ehci_hcd *ehci, struct pci_dev *pdev)  {
> >  	int			retval;
> > +	u32			val;
> > +	u32			thr;
> >
> >  	/* we expect static quirk code to handle the "extended capabilities"
> >  	 * (currently just BIOS handoff) allowed starting with EHCI 0.96 @@
> > -50,6 +74,22 @@ static int ehci_pci_reinit(struct ehci_hcd *ehci, struct
> pci_dev *pdev)
> >  	if (!retval)
> >  		ehci_dbg(ehci, "MWI active\n");
> >
> > +	/* Reset the threshold limit */
> > +	if (is_intel_quark_x1000(pdev)) {
> > +		/*
> > +			* In order to support the isochronous/interrupt
> > +			* transactions, 508 bytes should be used as
> > +			* max threshold values to maximize the
> > +			* performance
> > +		*/
> > +		thr = INTEL_QUARK_X1000_EHCI_THRESHOLD(
> > +			INTEL_QUARK_X1000_EHCI_MAX_PACKET_BUFFER_SIZE - 4
> > +			);
> > +		val = thr<<INTEL_QUARK_X1000_EHCI_THRESHOLD_OUT_SHIFT |
> > +				thr<<INTEL_QUARK_X1000_EHCI_THRESHOLD_IN_SHIFT;
> > +		ehci_writel(ehci, val, ehci->regs->intel_quark_x1000_insnreg01);
> 
> I saw what other people told you about the original patch version, and I
> disagree with them.  It is not necessary to include a detailed calculation like
> this, it only makes the code harder to read.  It will be better to have a single
> #define with a comment explaining it, like
> this:
> 
> /* Maximum usable threshold value is 0x7f dwords for both IN and OUT */
> #define INTEL_QUARK_X1000_EHCI_MAX_THRESHOLD	0x007f007f
> 
> Then here, just use INTEL_QUARK_X1000_EHCI_MAX_THRESHOLD instead of
> val.  The comment can simply say:
> 
> 	/*
> 	 * For the Intel QUARK X1000, raise the I/O threshold to the
> 	 * maximum usable value in order to improve performance.
> 	 */
> 
I think so also. It is not necessary to make so complicated. I will adopt your suggestions, it is more simple and clearly.

> Alan Stern

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