[snip]
> diff --git a/drivers/usb/host/xhci-sysfs.c b/drivers/usb/host/xhci-sysfs.c
> new file mode 100644
> index 0000000..0192ac4
> --- /dev/null
> +++ b/drivers/usb/host/xhci-sysfs.c
> @@ -0,0 +1,100 @@
> +/*
> + * sysfs interface for xHCI host controller driver
> + *
> + * Copyright (C) 2015 Intel Corp.
> + *
> + * Author: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +#include <linux/kernel.h>
> +
> +#include "xhci.h"
> +
> +/*
> + * Return the register offset of a extended capability specified
> + * by @cap_id. Return 0 if @cap_id capability is not supported or
> + * in error cases.
> + */
> +static int get_extended_capability_offset(struct xhci_hcd *xhci,
> + int cap_id)
> +{
> + u32 cap_reg;
> + unsigned long flags;
> + int offset;
> + void __iomem *base = (void __iomem *) xhci->cap_regs;
> + struct usb_hcd *hcd = xhci_to_hcd(xhci);
> + int time_to_leave = XHCI_EXT_MAX_CAPID;
> +
> + spin_lock_irqsave(&xhci->lock, flags);
> +
> + offset = xhci_find_next_cap_offset(base, XHCI_HCC_PARAMS_OFFSET);
> + if (!HCD_HW_ACCESSIBLE(hcd) || !offset) {
> + spin_unlock_irqrestore(&xhci->lock, flags);
> + return 0;
> + }
> +
> + while (time_to_leave--) {
> + cap_reg = readl(base + offset);
> +
> + if (XHCI_EXT_CAPS_ID(cap_reg) == cap_id)
> + break;
> +
> + offset = xhci_find_next_cap_offset(base, offset);
> + if (!offset)
> + break;
> + }
> +
> + spin_unlock_irqrestore(&xhci->lock, flags);
I'm not sure spin_lock is good and necessary here, also seems there's already
a function to find the cap offset:
xhci_find_ext_cap_by_id() in xhci-ext-caps.h
> +
> + return offset;
> +}
> +
Thanks
Dave
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