linux-kernel - Re: [PATCH 1/2] USB: HCD: Add driver hooks for (un)?map_urb_for

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Date:	Mon, 24 Jan 2011 11:32:36 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Robert Morell <rmorell@...dia.com>
cc:	David Brownell <dbrownell@...rs.sourceforge.net>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Benoit Goby <benoit@...roid.com>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Ming Lei <tom.leiming@...il.com>,
	Jacob Pan <jacob.jun.pan@...el.com>,
	Oliver Neukum <oliver@...kum.org>,
	Olof Johansson <olof@...om.net>,
	Erik Gilling <konkers@...roid.com>,
	Colin Cross <ccross@...roid.com>, <linux-usb@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-tegra@...r.kernel.org>
Subject: Re: [PATCH 1/2] USB: HCD: Add driver hooks for (un)?map_urb_for_dma

On Thu, 20 Jan 2011, Robert Morell wrote:

> Provide optional hooks for the host controller driver to override the
> default DMA mapping and unmapping routines.  In general, these shouldn't
> be necessary unless the host controller has special DMA requirements,
> such as alignment contraints.  If these are not specified, the
> general usb_hcd_(un)?map_urb_for_dma functions will be used instead.
> Also, pass the status to unmap_urb_for_dma so it can know whether the
> DMA buffer has been overwritten.
> 
> Finally, add a flag to be used by these implementations if they
> allocated a temporary buffer so it can be freed properly when unmapping.

Overall this looks fine.

> Signed-off-by: Robert Morell <rmorell@...dia.com>
> ---
> 
> The original patches renamed the exported symbols from
> (un)?map_urb_setup_for_dma to usb_hcd_(un)?map_urb_setup_for_dma, and continued
> to use the ones not prefixed by "usb_hcd" internally.  However, due to commit
> 1dae423dd9b which already exported unmap_urb_setup_for_dma as-is, I reworked
> this to export both unchanged and switch to the hooked_ prefix internally.

In fact, it would be preferable to have the "usb_" or "usb_hcd_" prefix
on exported symbols.  Can you write a third patch to go before these
two, which changes the existing usages?  I think there aren't too many.

> diff --git a/include/linux/usb/hcd.h b/include/linux/usb/hcd.h
> index 0b6e751..dc487ff 100644
> --- a/include/linux/usb/hcd.h
> +++ b/include/linux/usb/hcd.h
> @@ -233,6 +233,18 @@ struct hc_driver {
>  	int	(*urb_dequeue)(struct usb_hcd *hcd,
>  				struct urb *urb, int status);
>  
> +	/* (optional) these hooks allow an HCD to override the default DMA
> +	 * mapping and unmapping routines.  In general, they shouldn't be
> +	 * necessary unless the host controller has special DMA requirements,
> +	 * such as alignment contraints.  If these are not specified, the
> +         * general (un)?map_urb_for_dma functions will be used instead (and it
> +         * may be a good idea to call these functions in your HCD
> +         * implementation) */

Leading tabs vs. spaces.  Also, the style rules (not always rigorously
followed, but we may as well try) require the /* and */ to be on their
own lines.

Alan Stern

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