Revision 2be23c475af8ae4e25f8bab08d815b17593bd547 authored by Russell King on 08 September 2010, 15:27:56 UTC, committed by Russell King on 08 September 2010, 15:27:56 UTC
Dave Hylands reports:
| We've observed a problem with dma_alloc_writecombine when the system
| is under heavy load (heavy bus traffic). We've managed to reduce the
| problem to the following snippet, which is run from a kthread in a
| continuous loop:
|
| void *virtAddr;
| dma_addr_t physAddr;
| unsigned int numBytes = 256;
|
| for (;;) {
| virtAddr = dma_alloc_writecombine(NULL,
| numBytes, &physAddr, GFP_KERNEL);
| if (virtAddr == NULL) {
| printk(KERN_ERR "Running out of memory\n");
| break;
| }
|
| /* access DMA memory allocated */
| tmp = virtAddr;
| *tmp = 0x77;
|
| /* free DMA memory */
| dma_free_writecombine(NULL,
| numBytes, virtAddr, physAddr);
|
| ...sleep here...
| }
|
| By itself, the code will run forever with no issues. However, as we
| increase our bus traffic (typically using DMA) then the *tmp = 0x77
| line will eventually cause a page fault. If we add a small delay (a
| few microseconds) before the *tmp = 0x77, then we don't see a page
| fault, even under heavy load.
A dsb() is required after modifying the PTE entries to ensure that they
will always be visible. Add this dsb().
Reported-by: Dave Hylands <dhylands@gmail.com>
Tested-by: Dave Hylands <dhylands@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
1 parent a387f0f
at73c213.h
/*
* Driver for the AT73C213 16-bit stereo DAC on Atmel ATSTK1000
*
* Copyright (C) 2006 - 2007 Atmel Corporation
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation; either version 2 of the
* License, or (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
* 02111-1307, USA.
*
* The full GNU General Public License is included in this
* distribution in the file called COPYING.
*/
#ifndef _SND_AT73C213_H
#define _SND_AT73C213_H
/* DAC control register */
#define DAC_CTRL 0x00
#define DAC_CTRL_ONPADRV 7
#define DAC_CTRL_ONAUXIN 6
#define DAC_CTRL_ONDACR 5
#define DAC_CTRL_ONDACL 4
#define DAC_CTRL_ONLNOR 3
#define DAC_CTRL_ONLNOL 2
#define DAC_CTRL_ONLNIR 1
#define DAC_CTRL_ONLNIL 0
/* DAC left line in gain register */
#define DAC_LLIG 0x01
#define DAC_LLIG_LLIG 0
/* DAC right line in gain register */
#define DAC_RLIG 0x02
#define DAC_RLIG_RLIG 0
/* DAC Left Master Playback Gain Register */
#define DAC_LMPG 0x03
#define DAC_LMPG_LMPG 0
/* DAC Right Master Playback Gain Register */
#define DAC_RMPG 0x04
#define DAC_RMPG_RMPG 0
/* DAC Left Line Out Gain Register */
#define DAC_LLOG 0x05
#define DAC_LLOG_LLOG 0
/* DAC Right Line Out Gain Register */
#define DAC_RLOG 0x06
#define DAC_RLOG_RLOG 0
/* DAC Output Level Control Register */
#define DAC_OLC 0x07
#define DAC_OLC_RSHORT 7
#define DAC_OLC_ROLC 4
#define DAC_OLC_LSHORT 3
#define DAC_OLC_LOLC 0
/* DAC Mixer Control Register */
#define DAC_MC 0x08
#define DAC_MC_INVR 5
#define DAC_MC_INVL 4
#define DAC_MC_RMSMIN2 3
#define DAC_MC_RMSMIN1 2
#define DAC_MC_LMSMIN2 1
#define DAC_MC_LMSMIN1 0
/* DAC Clock and Sampling Frequency Control Register */
#define DAC_CSFC 0x09
#define DAC_CSFC_OVRSEL 4
/* DAC Miscellaneous Register */
#define DAC_MISC 0x0A
#define DAC_MISC_VCMCAPSEL 7
#define DAC_MISC_DINTSEL 4
#define DAC_MISC_DITHEN 3
#define DAC_MISC_DEEMPEN 2
#define DAC_MISC_NBITS 0
/* DAC Precharge Control Register */
#define DAC_PRECH 0x0C
#define DAC_PRECH_PRCHGPDRV 7
#define DAC_PRECH_PRCHGAUX1 6
#define DAC_PRECH_PRCHGLNOR 5
#define DAC_PRECH_PRCHGLNOL 4
#define DAC_PRECH_PRCHGLNIR 3
#define DAC_PRECH_PRCHGLNIL 2
#define DAC_PRECH_PRCHG 1
#define DAC_PRECH_ONMSTR 0
/* DAC Auxiliary Input Gain Control Register */
#define DAC_AUXG 0x0D
#define DAC_AUXG_AUXG 0
/* DAC Reset Register */
#define DAC_RST 0x10
#define DAC_RST_RESMASK 2
#define DAC_RST_RESFILZ 1
#define DAC_RST_RSTZ 0
/* Power Amplifier Control Register */
#define PA_CTRL 0x11
#define PA_CTRL_APAON 6
#define PA_CTRL_APAPRECH 5
#define PA_CTRL_APALP 4
#define PA_CTRL_APAGAIN 0
#endif /* _SND_AT73C213_H */
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