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https://github.com/edk2-porting/linux-next.git
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8066e51ae7
The chipsets with the isa_dma_bridge_buggy set do not stop DMA during DMA counter reads. The DMA counter is read in two 8-bit read steps on x86 platform. Sometimes, such reads happen during higher byte change so the lower byte is already decremented (rolled over) but the higher byte is not. It introduces an error that position is moved 256 bytes ahead of the true position. Thus, the next DMA position read can return a lower value then the previous read. If the DMA position is decreased (reversed) the ALSA subsystem is tricked into the playback underrun error and resets the playback. It results in a "pop" during a playback. Work around the issue by reading the counter twice and choosing a higher value. Signed-off-by: Krzysztof Helt <krzysztof.h1@wp.pl> Signed-off-by: Takashi Iwai <tiwai@suse.de>
117 lines
3.0 KiB
C
117 lines
3.0 KiB
C
/*
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* ISA DMA support functions
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* Copyright (c) by Jaroslav Kysela <perex@perex.cz>
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*
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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*
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*/
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/*
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* Defining following add some delay. Maybe this helps for some broken
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* ISA DMA controllers.
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*/
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#undef HAVE_REALLY_SLOW_DMA_CONTROLLER
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#include <sound/core.h>
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#include <asm/dma.h>
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/**
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* snd_dma_program - program an ISA DMA transfer
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* @dma: the dma number
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* @addr: the physical address of the buffer
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* @size: the DMA transfer size
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* @mode: the DMA transfer mode, DMA_MODE_XXX
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*
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* Programs an ISA DMA transfer for the given buffer.
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*/
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void snd_dma_program(unsigned long dma,
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unsigned long addr, unsigned int size,
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unsigned short mode)
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{
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unsigned long flags;
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flags = claim_dma_lock();
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disable_dma(dma);
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clear_dma_ff(dma);
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set_dma_mode(dma, mode);
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set_dma_addr(dma, addr);
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set_dma_count(dma, size);
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if (!(mode & DMA_MODE_NO_ENABLE))
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enable_dma(dma);
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release_dma_lock(flags);
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}
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EXPORT_SYMBOL(snd_dma_program);
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/**
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* snd_dma_disable - stop the ISA DMA transfer
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* @dma: the dma number
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*
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* Stops the ISA DMA transfer.
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*/
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void snd_dma_disable(unsigned long dma)
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{
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unsigned long flags;
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flags = claim_dma_lock();
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clear_dma_ff(dma);
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disable_dma(dma);
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release_dma_lock(flags);
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}
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EXPORT_SYMBOL(snd_dma_disable);
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/**
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* snd_dma_pointer - return the current pointer to DMA transfer buffer in bytes
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* @dma: the dma number
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* @size: the dma transfer size
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*
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* Returns the current pointer in DMA tranfer buffer in bytes
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*/
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unsigned int snd_dma_pointer(unsigned long dma, unsigned int size)
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{
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unsigned long flags;
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unsigned int result, result1;
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flags = claim_dma_lock();
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clear_dma_ff(dma);
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if (!isa_dma_bridge_buggy)
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disable_dma(dma);
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result = get_dma_residue(dma);
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/*
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* HACK - read the counter again and choose higher value in order to
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* avoid reading during counter lower byte roll over if the
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* isa_dma_bridge_buggy is set.
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*/
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result1 = get_dma_residue(dma);
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if (!isa_dma_bridge_buggy)
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enable_dma(dma);
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release_dma_lock(flags);
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if (unlikely(result < result1))
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result = result1;
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#ifdef CONFIG_SND_DEBUG
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if (result > size)
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snd_printk(KERN_ERR "pointer (0x%x) for DMA #%ld is greater than transfer size (0x%x)\n", result, dma, size);
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#endif
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if (result >= size || result == 0)
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return 0;
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else
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return size - result;
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}
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EXPORT_SYMBOL(snd_dma_pointer);
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