Re: [PATCH v5 1/2] dmaengine: 8250_mtk_dma: add Mediatek uart DMA support

[Sean Wang <sean.wang@kernel.org>]

Sorry for that I didn't have a full review at one time in the earlier version

       On Mon, Dec 10, 2018 at 9:37 PM Long Cheng
<long.cheng@mediatek.com> wrote:
>
> In DMA engine framework, add 8250 mtk dma to support it.

It looks like there are still many rooms to improve the description,
especially it's a totally new driver.

>
> Signed-off-by: Long Cheng <long.cheng@mediatek.com>
> ---
>  drivers/dma/mediatek/8250_mtk_dma.c |  830 +++++++++++++++++++++++++++++++++++
>  drivers/dma/mediatek/Kconfig        |   11 +
>  drivers/dma/mediatek/Makefile       |    1 +
>  3 files changed, 842 insertions(+)
>  create mode 100644 drivers/dma/mediatek/8250_mtk_dma.c
>
> diff --git a/drivers/dma/mediatek/8250_mtk_dma.c b/drivers/dma/mediatek/8250_mtk_dma.c
> new file mode 100644
> index 0000000..f79d180
> --- /dev/null
> +++ b/drivers/dma/mediatek/8250_mtk_dma.c
> @@ -0,0 +1,830 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Mediatek 8250 DMA driver.

MediaTek

> + *
> + * Copyright (c) 2018 MediaTek Inc.
> + * Author: Long Cheng <long.cheng@mediatek.com>
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/dmaengine.h>
> +#include <linux/dma-mapping.h>
> +#include <linux/err.h>
> +#include <linux/init.h>
> +#include <linux/interrupt.h>
> +#include <linux/list.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/of_dma.h>
> +#include <linux/of_device.h>
> +#include <linux/platform_device.h>
> +#include <linux/slab.h>
> +#include <linux/spinlock.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/iopoll.h>
> +
> +#include "../virt-dma.h"
> +
> +#define MTK_APDMA_DEFAULT_REQUESTS     127
> +#define MTK_APDMA_CHANNELS             (CONFIG_SERIAL_8250_NR_UARTS * 2)
> +
> +#define VFF_EN_B               BIT(0)
> +#define VFF_STOP_B             BIT(0)
> +#define VFF_FLUSH_B            BIT(0)
> +#define VFF_4G_SUPPORT_B       BIT(0)
> +#define VFF_RX_INT_EN0_B       BIT(0)  /*rx valid size >=  vff thre*/
> +#define VFF_RX_INT_EN1_B       BIT(1)
> +#define VFF_TX_INT_EN_B                BIT(0)  /*tx left size >= vff thre*/
> +#define VFF_WARM_RST_B         BIT(0)
> +#define VFF_RX_INT_FLAG_CLR_B  (BIT(0) | BIT(1))
> +#define VFF_TX_INT_FLAG_CLR_B  0
> +#define VFF_STOP_CLR_B         0
> +#define VFF_FLUSH_CLR_B                0
> +#define VFF_INT_EN_CLR_B       0
> +#define VFF_4G_SUPPORT_CLR_B   0
> +
> +/* interrupt trigger level for tx */
> +#define VFF_TX_THRE(n)         ((n) * 7 / 8)
> +/* interrupt trigger level for rx */
> +#define VFF_RX_THRE(n)         ((n) * 3 / 4)
> +
> +#define MTK_DMA_RING_SIZE      0xffffU
> +/* invert this bit when wrap ring head again*/
> +#define MTK_DMA_RING_WRAP      0x10000U
> +
> +#define VFF_INT_FLAG           0x00
> +#define VFF_INT_EN             0x04
> +#define VFF_EN                 0x08
> +#define VFF_RST                        0x0c
> +#define VFF_STOP               0x10
> +#define VFF_FLUSH              0x14
> +#define VFF_ADDR               0x1c
> +#define VFF_LEN                        0x24
> +#define VFF_THRE               0x28
> +#define VFF_WPT                        0x2c
> +#define VFF_RPT                        0x30
> +/*TX: the buffer size HW can read. RX: the buffer size SW can read.*/
> +#define VFF_VALID_SIZE         0x3c
> +/*TX: the buffer size SW can write. RX: the buffer size HW can write.*/
> +#define VFF_LEFT_SIZE          0x40
> +#define VFF_DEBUG_STATUS       0x50
> +#define VFF_4G_SUPPORT         0x54
> +
> +struct mtk_dmadev {
> +       struct dma_device ddev;
> +       void __iomem *mem_base[MTK_APDMA_CHANNELS];
> +       spinlock_t lock; /* dma dev lock */
> +       struct tasklet_struct task;

we can drop tasklet and instead allows descriptors to be handled as
fast as possible.
similar suggestions have been made in the other dmaengine [1] and mtk-hsdma.c

[1] https://lkml.org/lkml/2018/11/11/146

> +       struct list_head pending;
> +       struct clk *clk;
> +       unsigned int dma_requests;
> +       bool support_33bits;
> +       unsigned int dma_irq[MTK_APDMA_CHANNELS];
> +       struct mtk_chan *ch[MTK_APDMA_CHANNELS];
> +};
> +
> +struct mtk_chan {
> +       struct virt_dma_chan vc;
> +       struct list_head node;
> +       struct dma_slave_config cfg;
> +       void __iomem *base;
> +       struct mtk_dma_desc *desc;
> +
> +       bool stop;
> +       bool requested;
> +
> +       unsigned int rx_status;
> +};
> +
> +struct mtk_dma_sg {
> +       dma_addr_t addr;
> +       unsigned int en;                /* number of elements (24-bit) */
> +       unsigned int fn;                /* number of frames (16-bit) */
> +};
> +
> +struct mtk_dma_desc {
> +       struct virt_dma_desc vd;
> +       enum dma_transfer_direction dir;
> +
> +       unsigned int sglen;
> +       struct mtk_dma_sg sg[0];
> +
> +       unsigned int len;
> +};
> +
> +static inline struct mtk_dmadev *to_mtk_dma_dev(struct dma_device *d)
> +{
> +       return container_of(d, struct mtk_dmadev, ddev);
> +}
> +
> +static inline struct mtk_chan *to_mtk_dma_chan(struct dma_chan *c)
> +{
> +       return container_of(c, struct mtk_chan, vc.chan);
> +}
> +
> +static inline struct mtk_dma_desc *to_mtk_dma_desc
> +       (struct dma_async_tx_descriptor *t)
> +{
> +       return container_of(t, struct mtk_dma_desc, vd.tx);
> +}
> +
> +static void mtk_dma_chan_write(struct mtk_chan *c,
> +                              unsigned int reg, unsigned int val)
> +{
> +       writel(val, c->base + reg);
> +}
> +
> +static unsigned int mtk_dma_chan_read(struct mtk_chan *c, unsigned int reg)
> +{
> +       return readl(c->base + reg);
> +}
> +
> +static void mtk_dma_desc_free(struct virt_dma_desc *vd)
> +{
> +       struct dma_chan *chan = vd->tx.chan;
> +       struct mtk_chan *c = to_mtk_dma_chan(chan);
> +
> +       kfree(c->desc);
> +       c->desc = NULL;
> +}
> +
> +static void mtk_dma_tx_flush(struct dma_chan *chan)
> +{

If the user is only one, let's span the content into where the user is.

> +       struct mtk_chan *c = to_mtk_dma_chan(chan);
> +
> +       if (mtk_dma_chan_read(c, VFF_FLUSH) == 0U)
> +               mtk_dma_chan_write(c, VFF_FLUSH, VFF_FLUSH_B);
> +}
> +
> +static void mtk_dma_tx_write(struct dma_chan *chan)
> +{

If the user is only one, let's span the content into where the user is.

> +       struct mtk_chan *c = to_mtk_dma_chan(chan);
> +       unsigned int txcount = c->desc->len;
> +       unsigned int len, send, left, wpt, wrap;
> +
> +       len = mtk_dma_chan_read(c, VFF_LEN);
> +
> +       while ((left = mtk_dma_chan_read(c, VFF_LEFT_SIZE)) > 0U) {
> +               if (c->desc->len == 0U)

merge the condition back into the condition in while

> +                       break;
> +               send = min_t(unsigned int, left, c->desc->len);
> +               wpt = mtk_dma_chan_read(c, VFF_WPT);
> +               wrap = wpt & MTK_DMA_RING_WRAP ? 0U : MTK_DMA_RING_WRAP;
> +
> +               if ((wpt & (len - 1U)) + send < len)
> +                       mtk_dma_chan_write(c, VFF_WPT, wpt + send);
> +               else
> +                       mtk_dma_chan_write(c, VFF_WPT,
> +                                          ((wpt + send) & (len - 1U))
> +                                          | wrap);
> +
> +               c->desc->len -= send;

->len can be renamed to ->avail_len to say it's variable during the work

> +       }
> +
> +       if (txcount != c->desc->len) {
> +               mtk_dma_chan_write(c, VFF_INT_EN, VFF_TX_INT_EN_B);
> +               mtk_dma_tx_flush(chan);
> +       }
> +}
> +
> +static void mtk_dma_start_tx(struct mtk_chan *c)
> +{
> +       if (mtk_dma_chan_read(c, VFF_LEFT_SIZE) == 0U)
> +               mtk_dma_chan_write(c, VFF_INT_EN, VFF_TX_INT_EN_B);
> +       else
> +               mtk_dma_tx_write(&c->vc.chan);
> +
> +       c->stop = false;
> +}
> +
> +static void mtk_dma_get_rx_size(struct mtk_chan *c)
> +{

If the user is only one, let's span the content into where the user is.

> +       unsigned int rx_size = mtk_dma_chan_read(c, VFF_LEN);
> +       unsigned int rdptr, wrptr, wrreg, rdreg, count;

too much variable seems a little lousy, two variables are enough

unsigned int rd, wr;

> +
> +       rdreg = mtk_dma_chan_read(c, VFF_RPT);
> +       wrreg = mtk_dma_chan_read(c, VFF_WPT);
> +       rdptr = rdreg & MTK_DMA_RING_SIZE;
> +       wrptr = wrreg & MTK_DMA_RING_SIZE;

rd = mtk_dma_chan_read(c, VFF_RPT) & MTK_DMA_RING_SIZE;
wr = mtk_dma_chan_read(c, VFF_WPT) & MTK_DMA_RING_SIZE

> +       count = ((rdreg ^ wrreg) & MTK_DMA_RING_WRAP) ?
> +                       (wrptr + rx_size - rdptr) : (wrptr - rdptr);
> +
> +       c->rx_status = count;

drop the variable count and have a direct assignment

> +
> +       mtk_dma_chan_write(c, VFF_RPT, wrreg);
> +}
> +
> +static void mtk_dma_start_rx(struct mtk_chan *c)
> +{
> +       struct dma_chan *chan = &c->vc.chan;
> +       struct mtk_dmadev *mtkd = to_mtk_dma_dev(chan->device);
> +       struct mtk_dma_desc *d = c->desc;
> +
> +       if (mtk_dma_chan_read(c, VFF_VALID_SIZE) == 0U)
> +               return;
> +
> +       if (d && vchan_next_desc(&c->vc)) {
> +               mtk_dma_get_rx_size(c);
> +               list_del(&d->vd.node);
> +               vchan_cookie_complete(&d->vd);
> +       } else {
> +               spin_lock(&mtkd->lock);
> +               if (list_empty(&mtkd->pending))
> +                       list_add_tail(&c->node, &mtkd->pending);
> +               spin_unlock(&mtkd->lock);
> +               tasklet_schedule(&mtkd->task);
> +       }
> +}
> +
> +static void mtk_dma_reset(struct mtk_chan *c)
> +{

If the user is only one, let's span the content into where the user is.

> +       struct mtk_dmadev *mtkd = to_mtk_dma_dev(c->vc.chan.device);
> +       u32 status;
> +       int ret;
> +
> +       mtk_dma_chan_write(c, VFF_ADDR, 0);
> +       mtk_dma_chan_write(c, VFF_THRE, 0);
> +       mtk_dma_chan_write(c, VFF_LEN, 0);
> +       mtk_dma_chan_write(c, VFF_RST, VFF_WARM_RST_B);
> +
> +       ret = readx_poll_timeout(readl,
> +                                c->base + VFF_EN,
> +                                status, status == 0, 10, 100);
> +       if (ret) {
> +               dev_err(c->vc.chan.device->dev,
> +                               "dma reset: fail, timeout\n");
> +               return;
> +       }
> +
> +       if (c->cfg.direction == DMA_DEV_TO_MEM)
> +               mtk_dma_chan_write(c, VFF_RPT, 0);
> +       else if (c->cfg.direction == DMA_MEM_TO_DEV)
> +               mtk_dma_chan_write(c, VFF_WPT, 0);

using switch and case statement

> +
> +       if (mtkd->support_33bits)
> +               mtk_dma_chan_write(c, VFF_4G_SUPPORT, VFF_4G_SUPPORT_CLR_B);
> +}
> +
> +static void mtk_dma_stop(struct mtk_chan *c)

If the user is only one, let's span the content into where the user is.

> +{
> +       u32 status;
> +       int ret;
> +
> +       mtk_dma_chan_write(c, VFF_FLUSH, VFF_FLUSH_CLR_B);
> +       /* Wait for flush */
> +       ret = readx_poll_timeout(readl,
> +                                c->base + VFF_FLUSH,
> +                                status,
> +                                (status & VFF_FLUSH_B) != VFF_FLUSH_B,
> +                                10, 100);
> +       if (ret)
> +               dev_err(c->vc.chan.device->dev,
> +                       "dma stop: polling FLUSH fail, DEBUG=0x%x\n",
> +                       mtk_dma_chan_read(c, VFF_DEBUG_STATUS));
> +
> +       /*set stop as 1 -> wait until en is 0 -> set stop as 0*/
> +       mtk_dma_chan_write(c, VFF_STOP, VFF_STOP_B);
> +       ret = readx_poll_timeout(readl,
> +                                c->base + VFF_EN,
> +                                status, status == 0, 10, 100);
> +       if (ret)
> +               dev_err(c->vc.chan.device->dev,
> +                       "dma stop: polling VFF_EN fail, DEBUG=0x%x\n",
> +                       mtk_dma_chan_read(c, VFF_DEBUG_STATUS));
> +
> +       mtk_dma_chan_write(c, VFF_STOP, VFF_STOP_CLR_B);
> +       mtk_dma_chan_write(c, VFF_INT_EN, VFF_INT_EN_CLR_B);
> +
> +       if (c->cfg.direction == DMA_DEV_TO_MEM)
> +               mtk_dma_chan_write(c, VFF_INT_FLAG, VFF_RX_INT_FLAG_CLR_B);
> +       else
> +               mtk_dma_chan_write(c, VFF_INT_FLAG, VFF_TX_INT_FLAG_CLR_B);

using switch and case statement

> +
> +       c->stop = true;
> +}
> +
> +/*
> + * This callback schedules all pending channels. We could be more
> + * clever here by postponing allocation of the real DMA channels to
> + * this point, and freeing them when our virtual channel becomes idle.
> + *
> + * We would then need to deal with 'all channels in-use'
> + */
> +static void mtk_dma_sched(unsigned long data)
> +{

As at the initial be said, try to make descriptors submit as fast as
possible without involving in a tasklet. The same improvement had been
done at mtk-hsdma.c  so you could have a reference to it first if you
have no much idea of how to begin to improve.

> +       struct mtk_dmadev *mtkd = (struct mtk_dmadev *)data;
> +       struct virt_dma_desc *vd;
> +       struct mtk_chan *c;
> +       unsigned long flags;
> +       LIST_HEAD(head);
> +
> +       spin_lock_irq(&mtkd->lock);
> +       list_splice_tail_init(&mtkd->pending, &head);
> +       spin_unlock_irq(&mtkd->lock);
> +
> +       if (!list_empty(&head)) {
> +               c = list_first_entry(&head, struct mtk_chan, node);
> +
> +               spin_lock_irqsave(&c->vc.lock, flags);
> +               if (c->cfg.direction == DMA_DEV_TO_MEM) {
> +                       list_del_init(&c->node);
> +                       mtk_dma_start_rx(c);
> +               } else if (c->cfg.direction == DMA_MEM_TO_DEV) {
> +                       vd = vchan_next_desc(&c->vc);
> +                       c->desc = to_mtk_dma_desc(&vd->tx);
> +                       list_del_init(&c->node);
> +                       mtk_dma_start_tx(c);
> +               }
> +               spin_unlock_irqrestore(&c->vc.lock, flags);
> +       }
> +}
> +
> +static int mtk_dma_alloc_chan_resources(struct dma_chan *chan)
> +{
> +       struct mtk_dmadev *mtkd = to_mtk_dma_dev(chan->device);
> +       struct mtk_chan *c = to_mtk_dma_chan(chan);
> +       int ret = -EBUSY;
> +
> +       pm_runtime_get_sync(mtkd->ddev.dev);
> +
> +       if (!mtkd->ch[chan->chan_id]) {
> +               c->base = mtkd->mem_base[chan->chan_id]

mtkd->mem_base is unnecessary, we can directly decide c->base in the
driver probe stage

> +               mtkd->ch[chan->chan_id] = c;

mtkd->ch is also unnecessary, the core always pass struct dma_chan
*chan to each callback function

> +               ret = 1;

ret be 1 seems be wrong

> +       }
> +       c->requested = false;
> +       mtk_dma_reset(c);
> +
> +       return ret;
> +}
> +
> +static void mtk_dma_free_chan_resources(struct dma_chan *chan)
> +{
> +       struct mtk_dmadev *mtkd = to_mtk_dma_dev(chan->device);
> +       struct mtk_chan *c = to_mtk_dma_chan(chan);
> +
> +       if (c->requested) {
> +               c->requested = false;
> +               free_irq(mtkd->dma_irq[chan->chan_id], chan);

it makes not consistent because there are not request_irq present at
mtk_dma_alloc_chan_resources. but I'd prefer a  devm_request_irq is
being done
as the driver got probe.

> +       }
> +
> +       tasklet_kill(&mtkd->task);
> +       tasklet_kill(&c->vc.task);
> +
> +       c->base = NULL;
> +       mtkd->ch[chan->chan_id] = NULL;
> +       vchan_free_chan_resources(&c->vc);
> +
> +       pm_runtime_put_sync(mtkd->ddev.dev);
> +}
> +
> +static enum dma_status mtk_dma_tx_status(struct dma_chan *chan,
> +                                        dma_cookie_t cookie,
> +                                        struct dma_tx_state *txstate)
> +{
> +       struct mtk_chan *c = to_mtk_dma_chan(chan);
> +       enum dma_status ret;
> +       unsigned long flags;
> +
> +       if (!txstate)
> +               return DMA_ERROR;
> +
> +       ret = dma_cookie_status(chan, cookie, txstate);
> +       spin_lock_irqsave(&c->vc.lock, flags);
> +       if (ret == DMA_IN_PROGRESS) {
> +               c->rx_status = mtk_dma_chan_read(c, VFF_RPT)
> +                            & MTK_DMA_RING_SIZE;
> +               dma_set_residue(txstate, c->rx_status);
> +       } else if (ret == DMA_COMPLETE && c->cfg.direction == DMA_DEV_TO_MEM) {
> +               dma_set_residue(txstate, c->rx_status);
> +       } else {
> +               dma_set_residue(txstate, 0);
> +       }
> +       spin_unlock_irqrestore(&c->vc.lock, flags);
> +
> +       return ret;
> +}
> +
> +static struct dma_async_tx_descriptor *mtk_dma_prep_slave_sg
> +       (struct dma_chan *chan, struct scatterlist *sgl,
> +       unsigned int sglen,     enum dma_transfer_direction dir,
> +       unsigned long tx_flags, void *context)
> +{
> +       struct mtk_chan *c = to_mtk_dma_chan(chan);
> +       struct scatterlist *sgent;
> +       struct mtk_dma_desc *d;
> +       struct mtk_dma_sg *sg;
> +       unsigned int size, i, j, en;
> +
> +       en = 1;
> +
> +       if ((dir != DMA_DEV_TO_MEM) &&
> +               (dir != DMA_MEM_TO_DEV)) {
> +               dev_err(chan->device->dev, "bad direction\n");
> +               return NULL;
> +       }
> +
> +       /* Now allocate and setup the descriptor. */
> +       d = kzalloc(sizeof(*d) + sglen * sizeof(d->sg[0]), GFP_ATOMIC);
> +       if (!d)
> +               return NULL;
> +
> +       d->dir = dir;
> +
> +       j = 0;
> +       for_each_sg(sgl, sgent, sglen, i) {
> +               d->sg[j].addr = sg_dma_address(sgent);
> +               d->sg[j].en = en;
> +               d->sg[j].fn = sg_dma_len(sgent) / en;
> +               j++;
> +       }
> +
> +       d->sglen = j;
> +
> +       if (dir == DMA_MEM_TO_DEV) {
> +               for (size = i = 0; i < d->sglen; i++) {
> +                       sg = &d->sg[i];
> +                       size += sg->en * sg->fn;
> +               }
> +               d->len = size;
> +       }
> +

The driver always only handles data move for the single contiguous
area, but it seems the callback must provide the scatter-gather
function to the dmaegine. otherwise, why is the callback be called
device_prep_slave_sg?

> +       return vchan_tx_prep(&c->vc, &d->vd, tx_flags);
> +}
> +
> +static void mtk_dma_issue_pending(struct dma_chan *chan)
> +{
> +       struct mtk_chan *c = to_mtk_dma_chan(chan);
> +       struct virt_dma_desc *vd;
> +       struct mtk_dmadev *mtkd;
> +       unsigned long flags;
> +
> +       spin_lock_irqsave(&c->vc.lock, flags);
> +       if (c->cfg.direction == DMA_DEV_TO_MEM) {
> +               mtkd = to_mtk_dma_dev(chan->device);

mtkd can be dropped as it seems no users

> +               if (vchan_issue_pending(&c->vc) && !c->desc) {
> +                       vd = vchan_next_desc(&c->vc);
> +                       c->desc = to_mtk_dma_desc(&vd->tx);
> +               }
> +       } else if (c->cfg.direction == DMA_MEM_TO_DEV) {
> +               if (vchan_issue_pending(&c->vc) && !c->desc) {
> +                       vd = vchan_next_desc(&c->vc);
> +                       c->desc = to_mtk_dma_desc(&vd->tx);
> +                       mtk_dma_start_tx(c);
> +               }
> +       }
> +       spin_unlock_irqrestore(&c->vc.lock, flags);
> +}
> +
> +static irqreturn_t mtk_dma_rx_interrupt(int irq, void *dev_id)
> +{
> +       struct dma_chan *chan = (struct dma_chan *)dev_id;
> +       struct mtk_chan *c = to_mtk_dma_chan(chan);
> +       unsigned long flags;
> +
> +       spin_lock_irqsave(&c->vc.lock, flags);
> +       mtk_dma_chan_write(c, VFF_INT_FLAG, VFF_RX_INT_FLAG_CLR_B);
> +
> +       mtk_dma_start_rx(c);
> +
> +       spin_unlock_irqrestore(&c->vc.lock, flags);
> +
> +       return IRQ_HANDLED;
> +}
> +
> +static irqreturn_t mtk_dma_tx_interrupt(int irq, void *dev_id)
> +{
> +       struct dma_chan *chan = (struct dma_chan *)dev_id;
> +       struct mtk_dmadev *mtkd = to_mtk_dma_dev(chan->device);
> +       struct mtk_chan *c = to_mtk_dma_chan(chan);
> +       struct mtk_dma_desc *d = c->desc;
> +       unsigned long flags;
> +
> +       spin_lock_irqsave(&c->vc.lock, flags);
> +       if (d->len != 0U) {
> +               list_add_tail(&c->node, &mtkd->pending);
> +               tasklet_schedule(&mtkd->task);
> +       } else {
> +               list_del(&d->vd.node);
> +               vchan_cookie_complete(&d->vd);
> +       }
> +       spin_unlock_irqrestore(&c->vc.lock, flags);
> +
> +       mtk_dma_chan_write(c, VFF_INT_FLAG, VFF_TX_INT_FLAG_CLR_B);
> +
> +       return IRQ_HANDLED;
> +}
> +
> +static int mtk_dma_slave_config(struct dma_chan *chan,
> +                               struct dma_slave_config *cfg)
> +{
> +       struct mtk_chan *c = to_mtk_dma_chan(chan);
> +       struct mtk_dmadev *mtkd = to_mtk_dma_dev(c->vc.chan.device);
> +       int ret;
> +
> +       c->cfg = *cfg;
> +
> +       if (cfg->direction == DMA_DEV_TO_MEM) {
> +               unsigned int rx_len = cfg->src_addr_width * 1024;

it seems you should use cfg->src_port_window_size as the comments explains

* @src_port_window_size: The length of the register area in words the data need
 * to be accessed on the device side. It is only used for devices which is using
 * an area instead of a single register to receive the data. Typically the DMA
 * loops in this area in order to transfer the data.
 * @dst_port_window_size: same as src_port_window_size but for the destination
 * port.

> +
> +               mtk_dma_chan_write(c, VFF_ADDR, cfg->src_addr);
> +               mtk_dma_chan_write(c, VFF_LEN, rx_len);
> +               mtk_dma_chan_write(c, VFF_THRE, VFF_RX_THRE(rx_len));
> +               mtk_dma_chan_write(c,
> +                                  VFF_INT_EN, VFF_RX_INT_EN0_B
> +                                  | VFF_RX_INT_EN1_B);
> +               mtk_dma_chan_write(c, VFF_INT_FLAG, VFF_RX_INT_FLAG_CLR_B);
> +               mtk_dma_chan_write(c, VFF_EN, VFF_EN_B);

I'd prefer to move those channel interrupt enablement to
.device_alloc_chan_resources
and related disablement to .device_free_chan_resources

> +
> +               if (!c->requested) {
> +                       c->requested = true;
> +                       ret = request_irq(mtkd->dma_irq[chan->chan_id],
> +                                         mtk_dma_rx_interrupt,
> +                                         IRQF_TRIGGER_NONE,
> +                                         KBUILD_MODNAME, chan);

ISR registration usually happens as the driver got probe, it can give
the system more flexibility to manage such IRQ affinity on the fly.

> +                       if (ret < 0) {
> +                               dev_err(chan->device->dev, "Can't request rx dma IRQ\n");
> +                               return -EINVAL;
> +                       }
> +               }
> +       } else if (cfg->direction == DMA_MEM_TO_DEV)    {
> +               unsigned int tx_len = cfg->dst_addr_width * 1024;

Ditto as above, it seems you should use cfg->dst_port_window_size

> +
> +               mtk_dma_chan_write(c, VFF_ADDR, cfg->dst_addr);
> +               mtk_dma_chan_write(c, VFF_LEN, tx_len);
> +               mtk_dma_chan_write(c, VFF_THRE, VFF_TX_THRE(tx_len));
> +               mtk_dma_chan_write(c, VFF_INT_FLAG, VFF_TX_INT_FLAG_CLR_B);
> +               mtk_dma_chan_write(c, VFF_EN, VFF_EN_B);

ditto, I'd prefer to move those channel interrupt enablement to
.device_alloc_chan_resources and related disablement to
.device_free_chan_resources

> +
> +               if (!c->requested) {
> +                       c->requested = true;
> +                       ret = request_irq(mtkd->dma_irq[chan->chan_id],
> +                                         mtk_dma_tx_interrupt,
> +                                         IRQF_TRIGGER_NONE,
> +                                         KBUILD_MODNAME, chan);

ditto, we can request ISR with devm_request_irq in the driver got
probe and trim the c->request member

> +                       if (ret < 0) {
> +                               dev_err(chan->device->dev, "Can't request tx dma IRQ\n");
> +                               return -EINVAL;
> +                       }
> +               }
> +       }
> +
> +       if (mtkd->support_33bits)
> +               mtk_dma_chan_write(c, VFF_4G_SUPPORT, VFF_4G_SUPPORT_B);
> +
> +       if (mtk_dma_chan_read(c, VFF_EN) != VFF_EN_B) {
> +               dev_err(chan->device->dev,
> +                       "config dma dir[%d] fail\n", cfg->direction);
> +               return -EINVAL;
> +       }
> +
> +       return 0;
> +}
> +
> +static int mtk_dma_terminate_all(struct dma_chan *chan)
> +{
> +       struct mtk_chan *c = to_mtk_dma_chan(chan);
> +       unsigned long flags;
> +
> +       spin_lock_irqsave(&c->vc.lock, flags);
> +       list_del_init(&c->node);
> +       mtk_dma_stop(c);
> +       spin_unlock_irqrestore(&c->vc.lock, flags);
> +
> +       return 0;
> +}
> +
> +static int mtk_dma_device_pause(struct dma_chan *chan)
> +{
> +       /* just for check caps pass */
> +       return -EINVAL;

always return error code seems not the client driver wants us to do.

maybe if the hardware doesn't support pause, we can make a software
pause, that waits until all active descriptors in hardware done, then
disable interrupt and then stop handling the following vd in the
vchan.

> +}
> +
> +static int mtk_dma_device_resume(struct dma_chan *chan)
> +{
> +       /* just for check caps pass */
> +       return -EINVAL;

similar to the above

> +}
> +
> +static void mtk_dma_free(struct mtk_dmadev *mtkd)
> +{
> +       tasklet_kill(&mtkd->task);
> +       while (list_empty(&mtkd->ddev.channels) == 0) {
!list_empty(&mtkd->ddev.channels)
> +               struct mtk_chan *c = list_first_entry(&mtkd->ddev.channels,
> +                       struct mtk_chan, vc.chan.device_node);
> +
> +               list_del(&c->vc.chan.device_node);
> +               tasklet_kill(&c->vc.task);
> +               devm_kfree(mtkd->ddev.dev, c);

no need to call devm_kfree, the core would help do this

> +       }
> +}
> +
> +static const struct of_device_id mtk_uart_dma_match[] = {
> +       { .compatible = "mediatek,mt6577-uart-dma", },
> +       { /* sentinel */ },
> +};
> +MODULE_DEVICE_TABLE(of, mtk_uart_dma_match);
> +
> +static int mtk_apdma_probe(struct platform_device *pdev)
> +{
> +       struct mtk_dmadev *mtkd;
> +       struct resource *res;
> +       struct mtk_chan *c;
> +       unsigned int i;
> +       int rc;
> +
> +       mtkd = devm_kzalloc(&pdev->dev, sizeof(*mtkd), GFP_KERNEL);
> +       if (!mtkd)
> +               return -ENOMEM;
> +
> +       for (i = 0; i < MTK_APDMA_CHANNELS; i++) {
> +               res = platform_get_resource(pdev, IORESOURCE_MEM, i);
> +               if (!res)
> +                       return -ENODEV;
> +               mtkd->mem_base[i] = devm_ioremap_resource(&pdev->dev, res);
> +               if (IS_ERR(mtkd->mem_base[i]))
> +                       return PTR_ERR(mtkd->mem_base[i]);
> +       }
> +
> +       for (i = 0; i < MTK_APDMA_CHANNELS; i++) {
> +               mtkd->dma_irq[i] = platform_get_irq(pdev, i);
> +               if ((int)mtkd->dma_irq[i] < 0) {
> +                       dev_err(&pdev->dev, "failed to get IRQ[%d]\n", i);
> +                       return -EINVAL;
> +               }
> +       }
> +
> +       mtkd->clk = devm_clk_get(&pdev->dev, NULL);
> +       if (IS_ERR(mtkd->clk)) {
> +               dev_err(&pdev->dev, "No clock specified\n");
> +               return PTR_ERR(mtkd->clk);
> +       }
> +
> +       if (of_property_read_bool(pdev->dev.of_node, "dma-33bits")) {
> +               dev_info(&pdev->dev, "Support dma 33bits\n");
> +               mtkd->support_33bits = true;
> +       }
> +
> +       if (mtkd->support_33bits)
> +               rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(33));
> +       else
> +               rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));

 rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32 |
mtkd->support_33bits));

> +       if (rc)
> +               return rc;
> +
> +       dma_cap_set(DMA_SLAVE, mtkd->ddev.cap_mask);
> +       mtkd->ddev.device_alloc_chan_resources = mtk_dma_alloc_chan_resources;
> +       mtkd->ddev.device_free_chan_resources = mtk_dma_free_chan_resources;
> +       mtkd->ddev.device_tx_status = mtk_dma_tx_status;
> +       mtkd->ddev.device_issue_pending = mtk_dma_issue_pending;
> +       mtkd->ddev.device_prep_slave_sg = mtk_dma_prep_slave_sg;
> +       mtkd->ddev.device_config = mtk_dma_slave_config;
> +       mtkd->ddev.device_pause = mtk_dma_device_pause;
> +       mtkd->ddev.device_resume = mtk_dma_device_resume;
> +       mtkd->ddev.device_terminate_all = mtk_dma_terminate_all;
> +       mtkd->ddev.src_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_1_BYTE);
> +       mtkd->ddev.dst_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_1_BYTE);
> +       mtkd->ddev.directions = BIT(DMA_DEV_TO_MEM) | BIT(DMA_MEM_TO_DEV);
> +       mtkd->ddev.residue_granularity = DMA_RESIDUE_GRANULARITY_SEGMENT;
> +       mtkd->ddev.dev = &pdev->dev;
> +       INIT_LIST_HEAD(&mtkd->ddev.channels);
> +       INIT_LIST_HEAD(&mtkd->pending);
> +
> +       spin_lock_init(&mtkd->lock);
> +       tasklet_init(&mtkd->task, mtk_dma_sched, (unsigned long)mtkd);
> +
> +       mtkd->dma_requests = MTK_APDMA_DEFAULT_REQUESTS;
> +       if (of_property_read_u32(pdev->dev.of_node,
> +                                "dma-requests", &mtkd->dma_requests)) {
> +               dev_info(&pdev->dev,
> +                        "Missing dma-requests property, using %u.\n",
> +                        MTK_APDMA_DEFAULT_REQUESTS);
> +       }
> +
> +       for (i = 0; i < MTK_APDMA_CHANNELS; i++) {
> +               c = devm_kzalloc(mtkd->ddev.dev, sizeof(*c), GFP_KERNEL);
> +               if (!c)
> +                       goto err_no_dma;
> +
> +               c->vc.desc_free = mtk_dma_desc_free;
> +               vchan_init(&c->vc, &mtkd->ddev);
> +               INIT_LIST_HEAD(&c->node);
> +       }
> +
> +       pm_runtime_enable(&pdev->dev);
> +       pm_runtime_set_active(&pdev->dev);
> +
> +       rc = dma_async_device_register(&mtkd->ddev);
> +       if (rc)
> +               goto rpm_disable;
> +
> +       platform_set_drvdata(pdev, mtkd);
> +
> +       if (pdev->dev.of_node) {
> +               /* Device-tree DMA controller registration */
> +               rc = of_dma_controller_register(pdev->dev.of_node,
> +                                               of_dma_xlate_by_chan_id,
> +                                               mtkd);
> +               if (rc)
> +                       goto dma_remove;
> +       }
> +
> +       return rc;
> +
> +dma_remove:
> +       dma_async_device_unregister(&mtkd->ddev);
> +rpm_disable:
> +       pm_runtime_disable(&pdev->dev);
> +err_no_dma:
> +       mtk_dma_free(mtkd);
> +       return rc;
> +}
> +
> +static int mtk_apdma_remove(struct platform_device *pdev)
> +{
> +       struct mtk_dmadev *mtkd = platform_get_drvdata(pdev);
> +
> +       if (pdev->dev.of_node)
> +               of_dma_controller_free(pdev->dev.of_node);
> +
> +       pm_runtime_disable(&pdev->dev);
> +       pm_runtime_put_noidle(&pdev->dev);
> +
> +       dma_async_device_unregister(&mtkd->ddev);
> +
> +       mtk_dma_free(mtkd);
> +
> +       return 0;
> +}
> +
> +#ifdef CONFIG_PM_SLEEP
> +static int mtk_dma_suspend(struct device *dev)
> +{
> +       struct mtk_dmadev *mtkd = dev_get_drvdata(dev);
> +
> +       if (!pm_runtime_suspended(dev))
> +               clk_disable_unprepare(mtkd->clk);
> +
> +       return 0;
> +}
> +
> +static int mtk_dma_resume(struct device *dev)
> +{
> +       int ret;
> +       struct mtk_dmadev *mtkd = dev_get_drvdata(dev);
> +
> +       if (!pm_runtime_suspended(dev)) {
> +               ret = clk_prepare_enable(mtkd->clk);
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       return 0;
> +}
> +#endif /* CONFIG_PM_SLEEP */
> +
> +#ifdef CONFIG_PM
> +static int mtk_dma_runtime_suspend(struct device *dev)
> +{
> +       struct mtk_dmadev *mtkd = dev_get_drvdata(dev);
> +
> +       clk_disable_unprepare(mtkd->clk);
> +
> +       return 0;
> +}
> +
> +static int mtk_dma_runtime_resume(struct device *dev)
> +{
> +       int ret;
> +       struct mtk_dmadev *mtkd = dev_get_drvdata(dev);
> +
> +       ret = clk_prepare_enable(mtkd->clk);
> +       if (ret)
> +               return ret;
> +
> +       return 0;
> +}
> +#endif /* CONFIG_PM */
> +
> +static const struct dev_pm_ops mtk_dma_pm_ops = {
> +       SET_SYSTEM_SLEEP_PM_OPS(mtk_dma_suspend, mtk_dma_resume)
> +       SET_RUNTIME_PM_OPS(mtk_dma_runtime_suspend,
> +                          mtk_dma_runtime_resume, NULL)
> +};
> +
> +static struct platform_driver mtk_dma_driver = {

mtk_dma is much general and all functions and structures in the driver
should be all consistent.  I'd prefer to have all naming starts with
mtk_uart_apdma.

> +       .probe  = mtk_apdma_probe,

such  as
mtk_uart_apdma_probe

> +       .remove = mtk_apdma_remove,

mtk_uart_apdma_remove

> +       .driver = {
> +               .name           = KBUILD_MODNAME,
> +               .pm             = &mtk_dma_pm_ops,

mtk_uart_apdma_pm_ops

> +               .of_match_table = of_match_ptr(mtk_uart_dma_match),

mtk_uart_apdma_match

> +       },
> +};
> +
> +module_platform_driver(mtk_dma_driver);

mtk_uart_apdma_driver

> +
> +MODULE_DESCRIPTION("MediaTek UART APDMA Controller Driver");
> +MODULE_AUTHOR("Long Cheng <long.cheng@mediatek.com>");
> +MODULE_LICENSE("GPL v2");
> +
> diff --git a/drivers/dma/mediatek/Kconfig b/drivers/dma/mediatek/Kconfig
> index 27bac0b..d399624 100644
> --- a/drivers/dma/mediatek/Kconfig
> +++ b/drivers/dma/mediatek/Kconfig
> @@ -1,4 +1,15 @@
>
> +config DMA_MTK_UART

MTK_UART_APDMA to align the other drivers

> +       tristate "MediaTek SoCs APDMA support for UART"
> +       depends on OF && SERIAL_8250_MT6577
> +       select DMA_ENGINE
> +       select DMA_VIRTUAL_CHANNELS
> +       help
> +         Support for the UART DMA engine found on MediaTek MTK SoCs.
> +         when 8250 mtk uart is enabled, and if you want to using DMA,

8250 mtk uart should be changed to SERIAL_8250_MT6577 to be more intuitive

> +         you can enable the config. the DMA engine just only be used
> +         with MediaTek Socs.

SoCs

> +
>  config MTK_HSDMA
>         tristate "MediaTek High-Speed DMA controller support"
>         depends on ARCH_MEDIATEK || COMPILE_TEST
> diff --git a/drivers/dma/mediatek/Makefile b/drivers/dma/mediatek/Makefile
> index 6e778f8..2f2efd9 100644
> --- a/drivers/dma/mediatek/Makefile
> +++ b/drivers/dma/mediatek/Makefile
> @@ -1 +1,2 @@
> +obj-$(CONFIG_DMA_MTK_UART) += 8250_mtk_dma.o

obj-$(CONFIG_MTK_UART_APDMA) += mtk-uart-apdma.o
to align the other dirvers

>  obj-$(CONFIG_MTK_HSDMA) += mtk-hsdma.o
> --
> 1.7.9.5
>