linux/drivers/dma/dw/dw.c

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// SPDX-License-Identifier: GPL-2.0
// Copyright (C) 2007-2008 Atmel Corporation
// Copyright (C) 2010-2011 ST Microelectronics
// Copyright (C) 2013,2018 Intel Corporation
#include <linux/bitops.h>
#include <linux/dmaengine.h>
#include <linux/errno.h>
#include <linux/slab.h>
#include <linux/types.h>
#include "internal.h"
static void dw_dma_initialize_chan(struct dw_dma_chan *dwc)
{
struct dw_dma *dw = to_dw_dma(dwc->chan.device);
dmaengine: dw: Activate FIFO-mode for memory peripherals only CFGx.FIFO_MODE field controls a DMA-controller "FIFO readiness" criterion. In other words it determines when to start pushing data out of a DW DMAC channel FIFO to a destination peripheral or from a source peripheral to the DW DMAC channel FIFO. Currently FIFO-mode is set to one for all DW DMAC channels. It means they are tuned to flush data out of FIFO (to a memory peripheral or by accepting the burst transaction requests) when FIFO is at least half-full (except at the end of the block transfer, when FIFO-flush mode is activated) and are configured to get data to the FIFO when it's at least half-empty. Such configuration is a good choice when there is no slave device involved in the DMA transfers. In that case the number of bursts per block is less than when CFGx.FIFO_MODE = 0 and, hence, the bus utilization will improve. But the latency of DMA transfers may increase when CFGx.FIFO_MODE = 1, since DW DMAC will wait for the channel FIFO contents to be either half-full or half-empty depending on having the destination or the source transfers. Such latencies might be dangerous in case if the DMA transfers are expected to be performed from/to a slave device. Since normally peripheral devices keep data in internal FIFOs, any latency at some critical moment may cause one being overflown and consequently losing data. This especially concerns a case when either a peripheral device is relatively fast or the DW DMAC engine is relatively slow with respect to the incoming data pace. In order to solve problems, which might be caused by the latencies described above, let's enable the FIFO half-full/half-empty "FIFO readiness" criterion only for DMA transfers with no slave device involved. Thanks to the commit 99ba8b9b0d97 ("dmaengine: dw: Initialize channel before each transfer") we can freely do that in the generic dw_dma_initialize_chan() method. Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Link: https://lore.kernel.org/r/20200731200826.9292-3-Sergey.Semin@baikalelectronics.ru Signed-off-by: Vinod Koul <vkoul@kernel.org>
2020-07-31 20:08:23 +00:00
u32 cfghi = is_slave_direction(dwc->direction) ? 0 : DWC_CFGH_FIFO_MODE;
u32 cfglo = DWC_CFGL_CH_PRIOR(dwc->priority);
bool hs_polarity = dwc->dws.hs_polarity;
cfghi |= DWC_CFGH_DST_PER(dwc->dws.dst_id);
cfghi |= DWC_CFGH_SRC_PER(dwc->dws.src_id);
cfghi |= DWC_CFGH_PROTCTL(dw->pdata->protctl);
/* Set polarity of handshake interface */
cfglo |= hs_polarity ? DWC_CFGL_HS_DST_POL | DWC_CFGL_HS_SRC_POL : 0;
channel_writel(dwc, CFG_LO, cfglo);
channel_writel(dwc, CFG_HI, cfghi);
}
static void dw_dma_suspend_chan(struct dw_dma_chan *dwc, bool drain)
{
u32 cfglo = channel_readl(dwc, CFG_LO);
channel_writel(dwc, CFG_LO, cfglo | DWC_CFGL_CH_SUSP);
}
static void dw_dma_resume_chan(struct dw_dma_chan *dwc, bool drain)
{
u32 cfglo = channel_readl(dwc, CFG_LO);
channel_writel(dwc, CFG_LO, cfglo & ~DWC_CFGL_CH_SUSP);
}
static u32 dw_dma_bytes2block(struct dw_dma_chan *dwc,
size_t bytes, unsigned int width, size_t *len)
{
u32 block;
if ((bytes >> width) > dwc->block_size) {
block = dwc->block_size;
*len = dwc->block_size << width;
} else {
block = bytes >> width;
*len = bytes;
}
return block;
}
static size_t dw_dma_block2bytes(struct dw_dma_chan *dwc, u32 block, u32 width)
{
return DWC_CTLH_BLOCK_TS(block) << width;
}
static u32 dw_dma_prepare_ctllo(struct dw_dma_chan *dwc)
{
struct dma_slave_config *sconfig = &dwc->dma_sconfig;
u8 smsize = (dwc->direction == DMA_DEV_TO_MEM) ? sconfig->src_maxburst : 0;
u8 dmsize = (dwc->direction == DMA_MEM_TO_DEV) ? sconfig->dst_maxburst : 0;
u8 p_master = dwc->dws.p_master;
u8 m_master = dwc->dws.m_master;
u8 dms = (dwc->direction == DMA_MEM_TO_DEV) ? p_master : m_master;
u8 sms = (dwc->direction == DMA_DEV_TO_MEM) ? p_master : m_master;
return DWC_CTLL_LLP_D_EN | DWC_CTLL_LLP_S_EN |
DWC_CTLL_DST_MSIZE(dmsize) | DWC_CTLL_SRC_MSIZE(smsize) |
DWC_CTLL_DMS(dms) | DWC_CTLL_SMS(sms);
}
static void dw_dma_encode_maxburst(struct dw_dma_chan *dwc, u32 *maxburst)
{
/*
* Fix burst size according to dw_dmac. We need to convert them as:
* 1 -> 0, 4 -> 1, 8 -> 2, 16 -> 3.
*/
*maxburst = *maxburst > 1 ? fls(*maxburst) - 2 : 0;
}
static void dw_dma_set_device_name(struct dw_dma *dw, int id)
{
snprintf(dw->name, sizeof(dw->name), "dw:dmac%d", id);
}
static void dw_dma_disable(struct dw_dma *dw)
{
do_dw_dma_off(dw);
}
static void dw_dma_enable(struct dw_dma *dw)
{
do_dw_dma_on(dw);
}
int dw_dma_probe(struct dw_dma_chip *chip)
{
struct dw_dma *dw;
dw = devm_kzalloc(chip->dev, sizeof(*dw), GFP_KERNEL);
if (!dw)
return -ENOMEM;
/* Channel operations */
dw->initialize_chan = dw_dma_initialize_chan;
dw->suspend_chan = dw_dma_suspend_chan;
dw->resume_chan = dw_dma_resume_chan;
dw->prepare_ctllo = dw_dma_prepare_ctllo;
dw->encode_maxburst = dw_dma_encode_maxburst;
dw->bytes2block = dw_dma_bytes2block;
dw->block2bytes = dw_dma_block2bytes;
/* Device operations */
dw->set_device_name = dw_dma_set_device_name;
dw->disable = dw_dma_disable;
dw->enable = dw_dma_enable;
chip->dw = dw;
return do_dma_probe(chip);
}
EXPORT_SYMBOL_GPL(dw_dma_probe);
int dw_dma_remove(struct dw_dma_chip *chip)
{
return do_dma_remove(chip);
}
EXPORT_SYMBOL_GPL(dw_dma_remove);