Messages in this thread Patch in this message | | | Date | Thu, 20 Jan 2000 18:03:35 +0000 (GMT) | From | Tim Waugh <> | Subject | [patch] 2.3.40pre6: Take 3: avoid bounce buffers |
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Hi Linus,
Here's my third attempt to get this right. ;-) It tries to avoid a DMA bounce buffer when possible.
Tim. */
Index: linux/drivers/parport/parport_pc.c diff -u linux/drivers/parport/parport_pc.c:1.1.1.12 linux/drivers/parport/parport_pc.c:1.20 --- linux/drivers/parport/parport_pc.c:1.1.1.12 Tue Jan 18 11:16:06 2000 +++ linux/drivers/parport/parport_pc.c Thu Jan 20 18:03:59 2000 @@ -549,9 +549,23 @@ { int ret = 0; unsigned long dmaflag; - size_t left = length; + size_t left = length; const struct parport_pc_private *priv = port->physport->private_data; + unsigned long dma_addr; + size_t maxlen = 0x10000; /* max 64k per DMA transfer */ + /* above 16 MB we use a bounce buffer as ISA-DMA is not possible */ + if (buf+length <= MAX_DMA_ADDRESS) { + /* If it would cross a 64k boundary, cap it at the end. */ + if ((buf ^ (buf+length-1)) & ~0xffff) + maxlen = (0x10000 - buf) & 0xffff; + + dma_addr = virt_to_bus(buf); + } else { + dma_addr = virt_to_bus(priv->dma_buf); + maxlen = PAGE_SIZE; /* sizeof(priv->dma_buf) */ + } + port = port->physport; /* We don't want to be interrupted every character. */ @@ -566,16 +580,17 @@ size_t count = left; - if (count > PAGE_SIZE) - count = PAGE_SIZE; + if (count > maxlen) + count = maxlen; - memcpy(priv->dma_buf, buf, count); + if (maxlen == PAGE_SIZE) /* bounce buffer ! */ + memcpy(priv->dma_buf, buf, count); dmaflag = claim_dma_lock(); disable_dma(port->dma); clear_dma_ff(port->dma); set_dma_mode(port->dma, DMA_MODE_WRITE); - set_dma_addr(port->dma, virt_to_bus((volatile char *) priv->dma_buf)); + set_dma_addr(port->dma, dma_addr); set_dma_count(port->dma, count); /* Set DMA mode */
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