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Subject: Re: svn commit: r290610 - head/sys/x86/x86
To: =?UTF-8?Q?Roger_Pau_Monn=c3=a9?= <royger@FreeBSD.org>,
 src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
References: <201511091219.tA9CJwe7067036@repo.freebsd.org>
From: Hans Petter Selasky <hps@selasky.org>
Message-ID: <564091FF.8090605@selasky.org>
Date: Mon, 9 Nov 2015 13:30:55 +0100
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On 11/09/15 13:19, Roger Pau Monné wrote:
> +	if (dmat->common.flags & BUS_DMA_KEEP_PG_OFFSET) {
> +		/*
> +		 * If we have to keep the offset of each page this function
> +		 * is not suitable, switch back to bus_dmamap_load_ma_triv
> +		 * which is going to do the right thing in this case.
> +		 */
> +		error = bus_dmamap_load_ma_triv(dmat, map, ma, buflen, ma_offs,
> +		    flags, segs, segp);
> +		return (error);
> +	}

Hi,

There has been an update made to the USB stack, which is currently the 
only client of "BUS_DMA_KEEP_PG_OFFSET", which means this check can 
probably be skipped or relaxed a bit. The condition which must be 
fullfilled is:

#ifdef USB_DEBUG
         if (nseg > 1 &&
             ((segs->ds_addr + segs->ds_len) & (USB_PAGE_SIZE - 1)) !=
             ((segs + 1)->ds_addr & (USB_PAGE_SIZE - 1))) {
                 /*
                  * This check verifies there is no page offset hole
                  * between the first and second segment. See the
                  * BUS_DMA_KEEP_PG_OFFSET flag.
                  */
                 DPRINTFN(0, "Page offset was not preserved\n");
                 error = 1;
                 goto done;
         }
#endif

See: sys/dev/usb/usb_busdma.c

--HPS