Re: [PATCH v1 4/5] dmaengine: Add driver for NVIDIA Tegra AHB DMA controller
From: Dmitry Osipenko
Date: Tue Sep 26 2017 - 19:00:24 EST
On 27.09.2017 00:37, Jon Hunter wrote:
> Hi Dmitry,
>
> On 26/09/17 17:06, Dmitry Osipenko wrote:
>> Hi Jon,
>>
>> On 26.09.2017 17:45, Jon Hunter wrote:
>>> Hi Dmitry,
>>>
>>> On 26/09/17 00:22, Dmitry Osipenko wrote:
>>>> AHB DMA controller presents on Tegra20/30 SoC's, it supports transfers
>>>> memory <-> AHB bus peripherals as well as mem-to-mem transfers. Driver
>>>> doesn't yet implement transfers larger than 64K and scatter-gather
>>>> transfers that have NENT > 1, HW doesn't have native support for these
>>>> cases.
>>>>
>>>> Signed-off-by: Dmitry Osipenko <digetx@xxxxxxxxx>
>>>> ---
>>>> drivers/dma/Kconfig | 9 +
>>>> drivers/dma/Makefile | 1 +
>>>> drivers/dma/tegra20-ahb-dma.c | 679 ++++++++++++++++++++++++++++++++++++++++++
>>>> 3 files changed, 689 insertions(+)
>>>> create mode 100644 drivers/dma/tegra20-ahb-dma.c
>>>
>>> ...
>>>
>>>> diff --git a/drivers/dma/tegra20-ahb-dma.c b/drivers/dma/tegra20-ahb-dma.c
>>>> new file mode 100644
>>>> index 000000000000..8316d64e35e1
>>>> --- /dev/null
>>>> +++ b/drivers/dma/tegra20-ahb-dma.c
>>>> @@ -0,0 +1,679 @@
>>>> +/*
>>>> + * Copyright 2017 Dmitry Osipenko <digetx@xxxxxxxxx>
>>>> + *
>>>> + * This program is free software; you can redistribute it and/or modify it
>>>> + * under the terms and conditions of the GNU General Public License,
>>>> + * version 2, as published by the Free Software Foundation.
>>>> + *
>>>> + * This program is distributed in the hope 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, see <http://www.gnu.org/licenses/>.
>>>> + */
>>>> +
>>>> +#include <linux/clk.h>
>>>> +#include <linux/delay.h>
>>>> +#include <linux/interrupt.h>
>>>> +#include <linux/io.h>
>>>> +#include <linux/module.h>
>>>> +#include <linux/of_device.h>
>>>> +#include <linux/of_dma.h>
>>>> +#include <linux/platform_device.h>
>>>> +#include <linux/reset.h>
>>>> +#include <linux/slab.h>
>>>> +#include <linux/spinlock.h>
>>>> +
>>>> +#include "dmaengine.h"
>>>> +
>>>> +#define TEGRA_AHBDMA_CMD 0x0
>>>> +#define TEGRA_AHBDMA_CMD_ENABLE BIT(31)
>>>> +
>>>> +#define TEGRA_AHBDMA_IRQ_ENB_MASK 0x20
>>>> +#define TEGRA_AHBDMA_IRQ_ENB_CH(ch) BIT(ch)
>>>> +
>>>> +#define TEGRA_AHBDMA_CHANNEL_BASE(ch) (0x1000 + (ch) * 0x20)
>>>> +
>>>> +#define TEGRA_AHBDMA_CHANNEL_CSR 0x0
>>>> +#define TEGRA_AHBDMA_CHANNEL_ADDR_WRAP BIT(18)
>>>> +#define TEGRA_AHBDMA_CHANNEL_FLOW BIT(24)
>>>> +#define TEGRA_AHBDMA_CHANNEL_ONCE BIT(26)
>>>> +#define TEGRA_AHBDMA_CHANNEL_DIR_TO_XMB BIT(27)
>>>> +#define TEGRA_AHBDMA_CHANNEL_IE_EOC BIT(30)
>>>> +#define TEGRA_AHBDMA_CHANNEL_ENABLE BIT(31)
>>>> +#define TEGRA_AHBDMA_CHANNEL_REQ_SEL_SHIFT 16
>>>> +#define TEGRA_AHBDMA_CHANNEL_WCOUNT_MASK 0xFFFC
>>>> +
>>>> +#define TEGRA_AHBDMA_CHANNEL_STA 0x4
>>>> +#define TEGRA_AHBDMA_CHANNEL_IS_EOC BIT(30)
>>>> +
>>>> +#define TEGRA_AHBDMA_CHANNEL_AHB_PTR 0x10
>>>> +
>>>> +#define TEGRA_AHBDMA_CHANNEL_AHB_SEQ 0x14
>>>> +#define TEGRA_AHBDMA_CHANNEL_INTR_ENB BIT(31)
>>>> +#define TEGRA_AHBDMA_CHANNEL_AHB_BURST_SHIFT 24
>>>> +#define TEGRA_AHBDMA_CHANNEL_AHB_BURST_1 2
>>>> +#define TEGRA_AHBDMA_CHANNEL_AHB_BURST_4 3
>>>> +#define TEGRA_AHBDMA_CHANNEL_AHB_BURST_8 4
>>>> +
>>>> +#define TEGRA_AHBDMA_CHANNEL_XMB_PTR 0x18
>>>> +
>>>> +#define TEGRA_AHBDMA_BUS_WIDTH BIT(DMA_SLAVE_BUSWIDTH_4_BYTES)
>>>> +
>>>> +#define TEGRA_AHBDMA_DIRECTIONS BIT(DMA_DEV_TO_MEM) | \
>>>> + BIT(DMA_MEM_TO_DEV)
>>>> +
>>>> +struct tegra_ahbdma_tx_desc {
>>>> + struct dma_async_tx_descriptor desc;
>>>> + struct tasklet_struct tasklet;
>>>> + struct list_head node;
>>>
>>> Any reason why we cannot use the virt-dma framework for this driver? I
>>> would hope it would simplify the driver a bit.
>>>
>>
>> IIUC virt-dma is supposed to provide virtually unlimited number of channels.
>> I've looked at it and decided that it would just add unnecessary functionality
>> and, as a result, complexity. As I wrote in the cover-letter, it is supposed
>> that this driver would have only one consumer - the host1x. It shouldn't be
>> difficult to implement virt-dma later, if desired. But again it is very
>> unlikely that it would be needed.
>
> I think that the biggest benefit is that is simplifies the linked list
> management. See the tegra210-adma driver.
>
I'll take a more thorough look at it. Thank you for suggestion.
>>>> + enum dma_transfer_direction dir;
>>>> + dma_addr_t mem_paddr;
>>>> + unsigned long flags;
>>>> + size_t size;
>>>> + bool in_fly;
>>>> + bool cyclic;
>>>> +};
>>>> +
>>>> +struct tegra_ahbdma_chan {
>>>> + struct dma_chan dma_chan;
>>>> + struct list_head active_list;
>>>> + struct list_head pending_list;
>>>> + struct completion idling;
>>>> + void __iomem *regs;
>>>> + spinlock_t lock;
>>>> + unsigned int id;
>>>> +};
>>>> +
>>>> +struct tegra_ahbdma {
>>>> + struct tegra_ahbdma_chan channels[4];
>>>> + struct dma_device dma_dev;
>>>> + struct reset_control *rst;
>>>> + struct clk *clk;
>>>> + void __iomem *regs;
>>>> +};
>>>> +
>>>> +static inline struct tegra_ahbdma *to_ahbdma(struct dma_device *dev)
>>>> +{
>>>> + return container_of(dev, struct tegra_ahbdma, dma_dev);
>>>> +}
>>>> +
>>>> +static inline struct tegra_ahbdma_chan *to_ahbdma_chan(struct dma_chan *chan)
>>>> +{
>>>> + return container_of(chan, struct tegra_ahbdma_chan, dma_chan);
>>>> +}
>>>> +
>>>> +static inline struct tegra_ahbdma_tx_desc *to_ahbdma_tx_desc(
>>>> + struct dma_async_tx_descriptor *tx)
>>>> +{
>>>> + return container_of(tx, struct tegra_ahbdma_tx_desc, desc);
>>>> +}
>>>> +
>>>> +static void tegra_ahbdma_submit_tx(struct tegra_ahbdma_chan *chan,
>>>> + struct tegra_ahbdma_tx_desc *tx)
>>>> +{
>>>> + u32 csr;
>>>> +
>>>> + writel_relaxed(tx->mem_paddr,
>>>> + chan->regs + TEGRA_AHBDMA_CHANNEL_XMB_PTR);
>>>> +
>>>> + csr = readl_relaxed(chan->regs + TEGRA_AHBDMA_CHANNEL_CSR);
>>>> +
>>>> + csr &= ~TEGRA_AHBDMA_CHANNEL_WCOUNT_MASK;
>>>> + csr &= ~TEGRA_AHBDMA_CHANNEL_DIR_TO_XMB;
>>>> + csr |= TEGRA_AHBDMA_CHANNEL_ENABLE;
>>>> + csr |= TEGRA_AHBDMA_CHANNEL_IE_EOC;
>>>> + csr |= tx->size - sizeof(u32);
>>>> +
>>>> + if (tx->dir == DMA_DEV_TO_MEM)
>>>> + csr |= TEGRA_AHBDMA_CHANNEL_DIR_TO_XMB;
>>>> +
>>>> + if (!tx->cyclic)
>>>> + csr |= TEGRA_AHBDMA_CHANNEL_ONCE;
>>>> +
>>>> + writel_relaxed(csr, chan->regs + TEGRA_AHBDMA_CHANNEL_CSR);
>>>> +
>>>> + tx->in_fly = true;
>>>> +}
>>>> +
>>>> +static void tegra_ahbdma_tasklet(unsigned long data)
>>>> +{
>>>> + struct tegra_ahbdma_tx_desc *tx = (struct tegra_ahbdma_tx_desc *)data;
>>>> + struct dma_async_tx_descriptor *desc = &tx->desc;
>>>> +
>>>> + dmaengine_desc_get_callback_invoke(desc, NULL);
>>>> +
>>>> + if (!tx->cyclic && !dmaengine_desc_test_reuse(desc))
>>>> + kfree(tx);
>>>> +}
>>>> +
>>>> +static bool tegra_ahbdma_tx_completed(struct tegra_ahbdma_chan *chan,
>>>> + struct tegra_ahbdma_tx_desc *tx)
>>>> +{
>>>> + struct dma_async_tx_descriptor *desc = &tx->desc;
>>>> + bool reuse = dmaengine_desc_test_reuse(desc);
>>>> + bool interrupt = tx->flags & DMA_PREP_INTERRUPT;
>>>> + bool completed = !tx->cyclic;
>>>> +
>>>> + if (completed)
>>>> + dma_cookie_complete(desc);
>>>> +
>>>> + if (interrupt)
>>>> + tasklet_schedule(&tx->tasklet);
>>>> +
>>>> + if (completed) {
>>>> + list_del(&tx->node);
>>>> +
>>>> + if (reuse)
>>>> + tx->in_fly = false;
>>>> +
>>>> + if (!interrupt && !reuse)
>>>> + kfree(tx);
>>>> + }
>>>> +
>>>> + return completed;
>>>> +}
>>>> +
>>>> +static bool tegra_ahbdma_next_tx_issued(struct tegra_ahbdma_chan *chan)
>>>> +{
>>>> + struct tegra_ahbdma_tx_desc *tx;
>>>> +
>>>> + tx = list_first_entry_or_null(&chan->active_list,
>>>> + struct tegra_ahbdma_tx_desc,
>>>> + node);
>>>> + if (tx)
>>>> + tegra_ahbdma_submit_tx(chan, tx);
>>>> +
>>>> + return !!tx;
>>>> +}
>>>> +
>>>> +static void tegra_ahbdma_handle_channel(struct tegra_ahbdma_chan *chan)
>>>> +{
>>>> + struct tegra_ahbdma_tx_desc *tx;
>>>> + unsigned long flags;
>>>> + u32 status;
>>>> +
>>>> + status = readl_relaxed(chan->regs + TEGRA_AHBDMA_CHANNEL_STA);
>>>> + if (!(status & TEGRA_AHBDMA_CHANNEL_IS_EOC))
>>>> + return;
>>>> +
>>>> + writel_relaxed(TEGRA_AHBDMA_CHANNEL_IS_EOC,
>>>> + chan->regs + TEGRA_AHBDMA_CHANNEL_STA);
>>>> +
>>>> + spin_lock_irqsave(&chan->lock, flags);
>>>> +
>>>> + if (!completion_done(&chan->idling)) {
>>>> + tx = list_first_entry(&chan->active_list,
>>>> + struct tegra_ahbdma_tx_desc,
>>>> + node);
>>>> +
>>>> + if (tegra_ahbdma_tx_completed(chan, tx) &&
>>>> + !tegra_ahbdma_next_tx_issued(chan))
>>>> + complete_all(&chan->idling);
>>>> + }
>>>> +
>>>> + spin_unlock_irqrestore(&chan->lock, flags);
>>>> +}
>>>> +
>>>> +static irqreturn_t tegra_ahbdma_isr(int irq, void *dev_id)
>>>> +{
>>>> + struct tegra_ahbdma *tdma = dev_id;
>>>> + unsigned int i;
>>>> +
>>>> + for (i = 0; i < ARRAY_SIZE(tdma->channels); i++)
>>>> + tegra_ahbdma_handle_channel(&tdma->channels[i]);
>>>> +
>>>> + return IRQ_HANDLED;
>>>> +}
>>>> +
>>>> +static dma_cookie_t tegra_ahbdma_tx_submit(struct dma_async_tx_descriptor *desc)
>>>> +{
>>>> + struct tegra_ahbdma_tx_desc *tx = to_ahbdma_tx_desc(desc);
>>>> + struct tegra_ahbdma_chan *chan = to_ahbdma_chan(desc->chan);
>>>> + dma_cookie_t cookie;
>>>> +
>>>> + cookie = dma_cookie_assign(desc);
>>>> +
>>>> + spin_lock_irq(&chan->lock);
>>>> + list_add_tail(&tx->node, &chan->pending_list);
>>>> + spin_unlock_irq(&chan->lock);
>>>> +
>>>> + return cookie;
>>>> +}
>>>> +
>>>> +static int tegra_ahbdma_tx_desc_free(struct dma_async_tx_descriptor *desc)
>>>> +{
>>>> + kfree(to_ahbdma_tx_desc(desc));
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> +static struct dma_async_tx_descriptor *tegra_ahbdma_prep_slave_sg(
>>>> + struct dma_chan *chan,
>>>> + struct scatterlist *sgl,
>>>> + unsigned int sg_len,
>>>> + enum dma_transfer_direction dir,
>>>> + unsigned long flags,
>>>> + void *context)
>>>> +{
>>>> + struct tegra_ahbdma_tx_desc *tx;
>>>> +
>>>> + /* unimplemented */
>>>> + if (sg_len != 1 || sg_dma_len(sgl) > SZ_64K)
>>>> + return NULL;
>>>> +
>>>> + tx = kzalloc(sizeof(*tx), GFP_KERNEL);
>>>> + if (!tx)
>>>> + return NULL;
>>>> +
>>>> + dma_async_tx_descriptor_init(&tx->desc, chan);
>>>> +
>>>> + tx->desc.tx_submit = tegra_ahbdma_tx_submit;
>>>> + tx->desc.desc_free = tegra_ahbdma_tx_desc_free;
>>>> + tx->mem_paddr = sg_dma_address(sgl);
>>>> + tx->size = sg_dma_len(sgl);
>>>> + tx->flags = flags;
>>>> + tx->dir = dir;
>>>> +
>>>> + tasklet_init(&tx->tasklet, tegra_ahbdma_tasklet, (unsigned long)tx);
>>>> +
>>>> + return &tx->desc;
>>>> +}
>>>> +
>>>> +static struct dma_async_tx_descriptor *tegra_ahbdma_prep_dma_cyclic(
>>>> + struct dma_chan *chan,
>>>> + dma_addr_t buf_addr,
>>>> + size_t buf_len,
>>>> + size_t period_len,
>>>> + enum dma_transfer_direction dir,
>>>> + unsigned long flags)
>>>> +{
>>>> + struct tegra_ahbdma_tx_desc *tx;
>>>> +
>>>> + /* unimplemented */
>>>> + if (buf_len != period_len || buf_len > SZ_64K)
>>>> + return NULL;
>>>> +
>>>> + tx = kzalloc(sizeof(*tx), GFP_KERNEL);
>>>> + if (!tx)
>>>> + return NULL;
>>>> +
>>>> + dma_async_tx_descriptor_init(&tx->desc, chan);
>>>> +
>>>> + tx->desc.tx_submit = tegra_ahbdma_tx_submit;
>>>> + tx->mem_paddr = buf_addr;
>>>> + tx->size = buf_len;
>>>> + tx->flags = flags;
>>>> + tx->cyclic = true;
>>>> + tx->dir = dir;
>>>> +
>>>> + tasklet_init(&tx->tasklet, tegra_ahbdma_tasklet, (unsigned long)tx);
>>>> +
>>>> + return &tx->desc;
>>>> +}
>>>> +
>>>> +static void tegra_ahbdma_issue_pending(struct dma_chan *chan)
>>>> +{
>>>> + struct tegra_ahbdma_chan *ahbdma_chan = to_ahbdma_chan(chan);
>>>> + struct tegra_ahbdma_tx_desc *tx;
>>>> + struct list_head *entry, *tmp;
>>>> + unsigned long flags;
>>>> +
>>>> + spin_lock_irqsave(&ahbdma_chan->lock, flags);
>>>> +
>>>> + list_for_each_safe(entry, tmp, &ahbdma_chan->pending_list)
>>>> + list_move_tail(entry, &ahbdma_chan->active_list);
>>>> +
>>>> + if (completion_done(&ahbdma_chan->idling)) {
>>>> + tx = list_first_entry_or_null(&ahbdma_chan->active_list,
>>>> + struct tegra_ahbdma_tx_desc,
>>>> + node);
>>>> + if (tx) {
>>>> + tegra_ahbdma_submit_tx(ahbdma_chan, tx);
>>>> + reinit_completion(&ahbdma_chan->idling);
>>>> + }
>>>> + }
>>>> +
>>>> + spin_unlock_irqrestore(&ahbdma_chan->lock, flags);
>>>> +}
>>>> +
>>>> +static enum dma_status tegra_ahbdma_tx_status(struct dma_chan *chan,
>>>> + dma_cookie_t cookie,
>>>> + struct dma_tx_state *state)
>>>> +{
>>>> + struct tegra_ahbdma_chan *ahbdma_chan = to_ahbdma_chan(chan);
>>>> + struct tegra_ahbdma_tx_desc *tx;
>>>> + enum dma_status cookie_status;
>>>> + unsigned long flags;
>>>> + size_t residual;
>>>> + u32 status;
>>>> +
>>>> + spin_lock_irqsave(&ahbdma_chan->lock, flags);
>>>> +
>>>> + cookie_status = dma_cookie_status(chan, cookie, state);
>>>> + if (cookie_status != DMA_COMPLETE) {
>>>> + list_for_each_entry(tx, &ahbdma_chan->active_list, node) {
>>>> + if (tx->desc.cookie == cookie)
>>>> + goto found;
>>>> + }
>>>> + }
>>>> +
>>>> + goto unlock;
>>>> +
>>>> +found:
>>>> + if (tx->in_fly) {
>>>> + status = readl_relaxed(
>>>> + ahbdma_chan->regs + TEGRA_AHBDMA_CHANNEL_STA);
>>>> + status &= TEGRA_AHBDMA_CHANNEL_WCOUNT_MASK;
>>>> +
>>>> + residual = status;
>>>> + } else
>>>> + residual = tx->size;
>>>> +
>>>> + dma_set_residue(state, residual);
>>>> +
>>>> +unlock:
>>>> + spin_unlock_irqrestore(&ahbdma_chan->lock, flags);
>>>> +
>>>> + return cookie_status;
>>>> +}
>>>> +
>>>> +static int tegra_ahbdma_terminate_all(struct dma_chan *chan)
>>>> +{
>>>> + struct tegra_ahbdma_chan *ahbdma_chan = to_ahbdma_chan(chan);
>>>> + struct tegra_ahbdma_tx_desc *tx;
>>>> + struct list_head *entry, *tmp;
>>>> + u32 csr;
>>>> +
>>>> + spin_lock_irq(&ahbdma_chan->lock);
>>>> +
>>>> + csr = readl_relaxed(ahbdma_chan->regs + TEGRA_AHBDMA_CHANNEL_CSR);
>>>> + csr &= ~TEGRA_AHBDMA_CHANNEL_ENABLE;
>>>> +
>>>> + writel_relaxed(csr, ahbdma_chan->regs + TEGRA_AHBDMA_CHANNEL_CSR);
>>>> +
>>>> + list_for_each_safe(entry, tmp, &ahbdma_chan->active_list) {
>>>> + tx = list_entry(entry, struct tegra_ahbdma_tx_desc, node);
>>>> + list_del(entry);
>>>> + kfree(tx);
>>>> + }
>>>> +
>>>> + list_for_each_safe(entry, tmp, &ahbdma_chan->pending_list) {
>>>> + tx = list_entry(entry, struct tegra_ahbdma_tx_desc, node);
>>>> + list_del(entry);
>>>> + kfree(tx);
>>>> + }
>>>> +
>>>> + complete_all(&ahbdma_chan->idling);
>>>> +
>>>> + spin_unlock_irq(&ahbdma_chan->lock);
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> +static int tegra_ahbdma_config(struct dma_chan *chan,
>>>> + struct dma_slave_config *sconfig)
>>>> +{
>>>> + struct tegra_ahbdma_chan *ahbdma_chan = to_ahbdma_chan(chan);
>>>> + enum dma_transfer_direction dir = sconfig->direction;
>>>> + u32 burst, ahb_seq, ahb_addr;
>>>> +
>>>> + if (sconfig->src_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES ||
>>>> + sconfig->dst_addr_width != DMA_SLAVE_BUSWIDTH_4_BYTES)
>>>> + return -EINVAL;
>>>> +
>>>> + if (dir == DMA_DEV_TO_MEM) {
>>>> + burst = sconfig->src_maxburst;
>>>> + ahb_addr = sconfig->src_addr;
>>>> + } else {
>>>> + burst = sconfig->dst_maxburst;
>>>> + ahb_addr = sconfig->dst_addr;
>>>> + }
>>>> +
>>>> + switch (burst) {
>>>> + case 1: burst = TEGRA_AHBDMA_CHANNEL_AHB_BURST_1; break;
>>>> + case 4: burst = TEGRA_AHBDMA_CHANNEL_AHB_BURST_4; break;
>>>> + case 8: burst = TEGRA_AHBDMA_CHANNEL_AHB_BURST_8; break;
>>>> + default:
>>>> + return -EINVAL;
>>>> + }
>>>> +
>>>> + ahb_seq = burst << TEGRA_AHBDMA_CHANNEL_AHB_BURST_SHIFT;
>>>> + ahb_seq |= TEGRA_AHBDMA_CHANNEL_ADDR_WRAP;
>>>> + ahb_seq |= TEGRA_AHBDMA_CHANNEL_INTR_ENB;
>>>> +
>>>> + writel_relaxed(ahb_seq,
>>>> + ahbdma_chan->regs + TEGRA_AHBDMA_CHANNEL_AHB_SEQ);
>>>> +
>>>> + writel_relaxed(ahb_addr,
>>>> + ahbdma_chan->regs + TEGRA_AHBDMA_CHANNEL_AHB_PTR);
>>>> +
>>>> + return 0;
>>>> +}
>>>> +
>>>> +static void tegra_ahbdma_synchronize(struct dma_chan *chan)
>>>> +{
>>>> + wait_for_completion(&to_ahbdma_chan(chan)->idling);
>>>> +}
>>>> +
>>>> +static void tegra_ahbdma_free_chan_resources(struct dma_chan *chan)
>>>> +{
>>>> + struct tegra_ahbdma_chan *ahbdma_chan = to_ahbdma_chan(chan);
>>>> + struct tegra_ahbdma_tx_desc *tx;
>>>> + struct list_head *entry, *tmp;
>>>> +
>>>> + list_for_each_safe(entry, tmp, &ahbdma_chan->pending_list) {
>>>> + tx = list_entry(entry, struct tegra_ahbdma_tx_desc, node);
>>>> + list_del(entry);
>>>> + kfree(tx);
>>>> + }
>>>> +}
>>>> +
>>>> +static void tegra_ahbdma_init_channel(struct tegra_ahbdma *tdma,
>>>> + unsigned int chan_id)
>>>> +{
>>>> + struct tegra_ahbdma_chan *ahbdma_chan = &tdma->channels[chan_id];
>>>> + struct dma_chan *dma_chan = &ahbdma_chan->dma_chan;
>>>> + struct dma_device *dma_dev = &tdma->dma_dev;
>>>> +
>>>> + INIT_LIST_HEAD(&ahbdma_chan->active_list);
>>>> + INIT_LIST_HEAD(&ahbdma_chan->pending_list);
>>>> + init_completion(&ahbdma_chan->idling);
>>>> + spin_lock_init(&ahbdma_chan->lock);
>>>> + complete(&ahbdma_chan->idling);
>>>> +
>>>> + ahbdma_chan->regs = tdma->regs + TEGRA_AHBDMA_CHANNEL_BASE(chan_id);
>>>> + ahbdma_chan->id = chan_id;
>>>> +
>>>> + dma_cookie_init(dma_chan);
>>>> + dma_chan->device = dma_dev;
>>>> +
>>>> + list_add_tail(&dma_chan->device_node, &dma_dev->channels);
>>>> +}
>>>> +
>>>> +static struct dma_chan *tegra_ahbdma_of_xlate(struct of_phandle_args *dma_spec,
>>>> + struct of_dma *ofdma)
>>>> +{
>>>> + struct tegra_ahbdma *tdma = ofdma->of_dma_data;
>>>> + struct dma_chan *chan;
>>>> + u32 csr;
>>>> +
>>>> + chan = dma_get_any_slave_channel(&tdma->dma_dev);
>>>> + if (!chan)
>>>> + return NULL;
>>>> +
>>>> + /* enable channels flow control */
>>>> + if (dma_spec->args_count == 1) {
>>>
>>> The DT doc says #dma-cells should be '1' and so if not equal 1, is this
>>> not an error?
>>>
>>
>> I wanted to differentiate slave/master modes here. But if we'd want to add
>> TRIG_SEL as another cell, then it probably would worth to implement a custom DMA
>> configure options, like documentation suggests - to wrap generic
>> dma_slave_config into the custom one. On the other hand that probably would add
>> an unused functionality to the driver.
>>
>>>> + csr = TEGRA_AHBDMA_CHANNEL_FLOW;
>>>> + csr |= dma_spec->args[0] << TEGRA_AHBDMA_CHANNEL_REQ_SEL_SHIFT;
>>>
>>> What about the TRIG_REQ field?
>>>
>>
>> Not implemented, there is no test case for it yet.
>>
>>>> +
>>>> + writel_relaxed(csr,
>>>> + to_ahbdma_chan(chan)->regs + TEGRA_AHBDMA_CHANNEL_CSR);
>>>> + }
>>>> +
>>>> + return chan;
>>>> +}
>>>> +
>>>> +static int tegra_ahbdma_init_hw(struct tegra_ahbdma *tdma, struct device *dev)
>>>> +{
>>>> + int err;
>>>> +
>>>> + err = reset_control_assert(tdma->rst);
>>>> + if (err) {
>>>> + dev_err(dev, "Failed to assert reset: %d\n", err);
>>>> + return err;
>>>> + }
>>>> +
>>>> + err = clk_prepare_enable(tdma->clk);
>>>> + if (err) {
>>>> + dev_err(dev, "Failed to enable clock: %d\n", err);
>>>> + return err;
>>>> + }
>>>> +
>>>> + usleep_range(1000, 2000);
>>>> +
>>>> + err = reset_control_deassert(tdma->rst);
>>>> + if (err) {
>>>> + dev_err(dev, "Failed to deassert reset: %d\n", err);
>>>> + return err;
>>>> + }
>>>> +
>>>> + writel_relaxed(TEGRA_AHBDMA_CMD_ENABLE, tdma->regs + TEGRA_AHBDMA_CMD);
>>>> +
>>>> + writel_relaxed(TEGRA_AHBDMA_IRQ_ENB_CH(0) |
>>>> + TEGRA_AHBDMA_IRQ_ENB_CH(1) |
>>>> + TEGRA_AHBDMA_IRQ_ENB_CH(2) |
>>>> + TEGRA_AHBDMA_IRQ_ENB_CH(3),
>>>> + tdma->regs + TEGRA_AHBDMA_IRQ_ENB_MASK);
>>>> +
>>>> + return 0;
>>>> +}
>>>
>>> Personally I would use the pm_runtime callbacks for this sort of thing
>>> and ...
>>>
>>
>> I decided that it probaby would be better to implement PM later if needed. I'm
>> not sure whether DMA controller consumes any substantial amounts of power while
>> idling. If it's not, why bother? Unnecessary power managment would just cause
>> CPU to waste its cycles (and power) doing PM.
>
> Yes it probably does not but it is easy to do and so even though there
> are probably a ton of other clocks left running, I still think it is
> good practice.
>
Okay, I'll take a look into implementing PM. Disabling AHBDMA clock won't stop
the actual clock, but only gate it to the controller.
Thank you for the comments!
--
Dmitry