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Message-ID: <1544700985.28871.26.camel@mhfsdcap03>
Subject: Re: [PATCH v5 1/2] dmaengine: 8250_mtk_dma: add Mediatek uart DMA
 support
From:   Long Cheng <long.cheng@mediatek.com>
To:     Sean Wang <sean.wang@kernel.org>
CC:     <vkoul@kernel.org>, <robh+dt@kernel.org>, <mark.rutland@arm.com>,
        <ryder.lee@mediatek.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        <dan.j.williams@intel.com>, <gregkh@linuxfoundation.org>,
        <jslaby@suse.com>,
        "Sean Wang =?UTF-8?Q?=28=E7=8E=8B=E5=BF=97=E4=BA=98=29?=" 
        <sean.wang@mediatek.com>, <dmaengine@vger.kernel.org>,
        <devicetree@vger.kernel.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-mediatek@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <linux-serial@vger.kernel.org>,
        <srv_heupstream@mediatek.com>, <yingjoe.chen@mediatek.com>,
        YT Shen <yt.shen@mediatek.com>,
        Long Cheng <long.cheng@mediatek.com>
Date:   Thu, 13 Dec 2018 19:36:25 +0800
In-Reply-To: <CAGp9LzqB=hzkOHZqa-ZzRLcJujU--7gxYZczXiEj3DiH+FmhbQ@mail.gmail.com>
References: <1544506645-27979-1-git-send-email-long.cheng@mediatek.com>
         <1544506645-27979-2-git-send-email-long.cheng@mediatek.com>
         <CAGp9LzqB=hzkOHZqa-ZzRLcJujU--7gxYZczXiEj3DiH+FmhbQ@mail.gmail.com>
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On Tue, 2018-12-11 at 15:12 -0800, Sean Wang wrote:
> 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
> 

OK, i will remove these, and improve it.

> [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?
> 

because in 8250 UART native code, call the device_prep_slave_sg. we just
use one ring buffer.

> > +       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.
> 

in 8250 UART native code, will set the parameter. if want to modify
this, i think that maybe at next kernel release, we can modify it. i
suggest that not modify it at this patch. because it relate of 8250 uart
code. thanks.

> > +
> > +               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
> 

i think that, first need set the config to HW, and the enable the DMA. 

> > +
> > +               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.
> 

i will move the request irq to alloc channel.

> > +                       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.
> 
> > +}

the code can't run. just for 8250 native code to check the function
pointer. in the future, if the function useful, we can realize. thanks.

> > +
> > +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.
> 

the function name and parameters' name, i will modify it. but before the
8250_mtk.c and the Doc. are recorded. if modify file name and Kconfig,
will bring about the disorder. i suggest that after the patch is
recorded, modify this. thanks.

> > +       .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
> >