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Date: Wed, 22 Dec 2010 12:22:40 +0000 From: Russell King - ARM Linux <linux@....linux.org.uk> To: Linus Walleij <linus.walleij@...ricsson.com> Cc: Viresh Kumar <viresh.kumar@...com>, Kukjin Kim <kgene.kim@...sung.com>, yuanyabin1978@...a.com, linux-kernel@...r.kernel.org, Ben Dooks <ben-linux@...ff.org>, Peter Pearse <peter.pearse@....com>, Dan Williams <dan.j.williams@...el.com>, linux-arm-kernel@...ts.infradead.org, Alessandro Rubini <rubini@...pv.it> Subject: Re: [PATCH 06/13] DMAENGINE: driver for the ARM PL080/PL081 PrimeCells On Tue, Dec 21, 2010 at 06:20:37PM +0000, Russell King - ARM Linux wrote: > Having just looked at this while trying to undo the DMA API abuses > in the PL011 UART driver, I'm getting rather frustrated with this > code. Right, just tried this on the Versatile PB/926, which has a PL080. The result is DMA errors. This turns out to be the hard-coding of which AHB bus is used. You can't hard-code this information into the driver - it's part of the bus matrix configuration. On Versatile PB/926, the two AHB buses have different memory maps - see DUI0224 page 3-13: * DMA0 (which is DMA AHB M1) has access to the APB peripherals but not the system memory. * DMA1 (which is DMA AHB M2) has access to the system memory but none of the APB peripherals. Throwing in #ifdef's to sort this out resolves the problem on the PB/926. Looking at the driver code too, I'm having a hard time understanding it, probably because of the use of "master" and "slave" - I don't think this has anything to do with which AHB master is used. The comments against pl08x_choose_master_bus() seem to imply that it controls which AHB master is used, but it has no apparant effect on that. I don't think this function does anything like that anymore. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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