linux-kernel - RE: [PATCH 1/1] mfd: omap-usb-host: Fix USB device detection problems on OMAP4 Panda

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Date:	Fri, 29 Nov 2013 13:17:48 -0000
From:	"David Laight" <David.Laight@...LAB.COM>
To:	"Roger Quadros" <rogerq@...com>, <lee.jones@...aro.org>,
	<sameo@...ux.intel.com>
Cc:	<tomi.valkeinen@...com>, <balbi@...com>, <sr@...x.de>,
	<ljkenny.mailinglists@...il.com>, <linux-omap@...r.kernel.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<stable@...r.kernel.org>
Subject: RE: [PATCH 1/1] mfd: omap-usb-host: Fix USB device detection problems on OMAP4 Panda

> From: Of Roger Quadros
> With u-boot 2013.10, USB devices are sometimes not detected
> on OMAP4 Panda. To make us independent of what bootloader does
> with the USB Host module, we must RESET it to get it to a known
> good state. This patch Soft RESETs the USB Host module.
...
> +++ b/drivers/mfd/omap-usb-host.c
> @@ -43,14 +43,18 @@
>  /* UHH Register Set */
>  #define	OMAP_UHH_REVISION				(0x00)
>  #define	OMAP_UHH_SYSCONFIG				(0x10)
> -#define	OMAP_UHH_SYSCONFIG_MIDLEMODE			(1 << 12)
> +#define	OMAP_UHH_SYSCONFIG_MIDLEMASK			(3 << 12)
> +#define OMAP_UHH_SYSCONFIG_MIDLESHIFT			(12)

(tab/space issue)

Wouldn't it be clearer to define these in the opposite order with:
+#define	OMAP_UHH_SYSCONFIG_MIDLEMASK			(3 << OMAP_UHH_SYSCONFIG_MIDLESHIFT)

... 
> +static void omap_usbhs_rev1_reset(struct device *dev)
> +{
> +	struct usbhs_hcd_omap *omap = dev_get_drvdata(dev);
> +	u32 reg;
> +	unsigned long timeout;
> +
> +	reg = usbhs_read(omap->uhh_base, OMAP_UHH_SYSCONFIG);
> +
> +	/* Soft Reset */
> +	usbhs_write(omap->uhh_base, OMAP_UHH_SYSCONFIG,
> +		    reg | OMAP_UHH_SYSCONFIG_SOFTRESET);
> +
> +	timeout = jiffies + msecs_to_jiffies(100);
> +	while (!(usbhs_read(omap->uhh_base, OMAP_UHH_SYSSTATUS)
> +			& OMAP_UHH_SYSSTATUS_RESETDONE)) {
> +		cpu_relax();
> +
> +		if (time_after(jiffies, timeout)) {
> +			dev_err(dev, "Soft RESET operation timed out\n");
> +			break;
> +		}
> +	}
> +
> +	/* Set No-Standby */
> +	reg &= ~OMAP_UHH_SYSCONFIG_MIDLEMASK;
> +	reg |= OMAP_UHH_SYSCONFIG_MIDLE_NOSTANDBY
> +		<< OMAP_UHH_SYSCONFIG_MIDLESHIFT;
> +
> +	/* Set No-Idle */
> +	reg &= ~OMAP_UHH_SYSCONFIG_SIDLEMASK;
> +	reg |= OMAP_UHH_SYSCONFIG_SIDLE_NOIDLE
> +		<< OMAP_UHH_SYSCONFIG_SIDLESHIFT;

Why not pass in the mask and value and avoid replicating the
entire function. I can't see any other significant differences,
the udelay(2) won't be significant.

I'm not sure of the context this code runs in, but if the reset
is likely to take a significant portion of the 100ms timeout
period, why not just sleep for a few ms between status polls.

	David




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