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In-Reply-To: <1545739611.28871.77.camel@mhfsdcap03>
From:   Nicolas Boichat <drinkcat@chromium.org>
Date:   Wed, 26 Dec 2018 08:05:46 +0800
Message-ID: <CANMq1KDtUgOUFRy-TyQK0EmbpXGtLEVo9Mqg1Hvs0JoL9NrFyQ@mail.gmail.com>
Subject: Re: [PATCH v7 1/2] dmaengine: 8250_mtk_dma: add MediaTek uart DMA support
To:     Long Cheng <long.cheng@mediatek.com>
Cc:     Vinod Koul <vkoul@kernel.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Ryder Lee <ryder.lee@mediatek.com>,
        Sean Wang <sean.wang@kernel.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jiri Slaby <jslaby@suse.com>,
        Sean Wang <sean.wang@mediatek.com>, dmaengine@vger.kernel.org,
        devicetree@vger.kernel.org,
        linux-arm Mailing List <linux-arm-kernel@lists.infradead.org>,
        linux-mediatek@lists.infradead.org,
        lkml <linux-kernel@vger.kernel.org>,
        linux-serial@vger.kernel.org, srv_heupstream@mediatek.com,
        Yingjoe Chen <yingjoe.chen@mediatek.com>,
        YT Shen <yt.shen@mediatek.com>
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On Tue, Dec 25, 2018 at 8:06 PM Long Cheng <long.cheng@mediatek.com> wrote:
>
> Thanks for your comments.
>
> On Tue, 2018-12-25 at 15:16 +0800, Nicolas Boichat wrote:
> > Not a full review, a few comments below.
> >
> > Thanks,
> >
>
> would you like help to full review at this version patch?  and then i
> can modify these at next version patch. thanks.

Added a few more comments ,-)

> > On Tue, Dec 25, 2018 at 9:27 AM Long Cheng <long.cheng@mediatek.com> wrote:
> > >
> > > In DMA engine framework, add 8250 uart dma to support MediaTek uart.
> > > If MediaTek uart enabled(SERIAL_8250_MT6577), and want to improve
> > > the performance, can enable the function.
> > >
> > > Signed-off-by: Long Cheng <long.cheng@mediatek.com>
> > > ---
> > >  drivers/dma/mediatek/8250_mtk_dma.c |  694 +++++++++++++++++++++++++++++++++++
> > >  drivers/dma/mediatek/Kconfig        |   11 +
> > >  drivers/dma/mediatek/Makefile       |    1 +
> > >  3 files changed, 706 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..c4090f2
> > > --- /dev/null
> > > +++ b/drivers/dma/mediatek/8250_mtk_dma.c
> > > @@ -0,0 +1,694 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/*
> > > + * MediaTek 8250 DMA driver.
> > > + *
> > > + * 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>
> >
> > Alphabetical order.
>
> ok, i will order.
>
> >
> > > +
> > > +#include "../virt-dma.h"
> > > +
> > > +#define MTK_UART_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_UART_APDMA_RING_SIZE       0xffffU
> > > +/* invert this bit when wrap ring head again*/
> > > +#define MTK_UART_APDMA_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_uart_apdmadev {
> > > +       struct dma_device ddev;
> > > +       struct clk *clk;
> > > +       bool support_33bits;
> > > +       unsigned int dma_irq[MTK_UART_APDMA_CHANNELS];
> > > +};
> > > +
> > > +struct mtk_uart_apdma_desc {
> > > +       struct virt_dma_desc vd;
> > > +
> > > +       unsigned int avail_len;
> > > +};
> > > +
> > > +struct mtk_chan {
> > > +       struct virt_dma_chan vc;
> > > +       struct dma_slave_config cfg;
> > > +       void __iomem *base;
> > > +       struct mtk_uart_apdma_desc *desc;
> > > +
> > > +       bool requested;
> > > +
> > > +       unsigned int rx_status;
> > > +};
> > > +
> > > +static inline struct mtk_uart_apdmadev *
> > > +to_mtk_uart_apdma_dev(struct dma_device *d)
> > > +{
> > > +       return container_of(d, struct mtk_uart_apdmadev, ddev);
> > > +}
> > > +
> > > +static inline struct mtk_chan *to_mtk_uart_apdma_chan(struct dma_chan *c)
> > > +{
> > > +       return container_of(c, struct mtk_chan, vc.chan);
> > > +}
> > > +
> > > +static inline struct mtk_uart_apdma_desc *to_mtk_uart_apdma_desc
> > > +       (struct dma_async_tx_descriptor *t)
> > > +{
> > > +       return container_of(t, struct mtk_uart_apdma_desc, vd.tx);
> > > +}
> > > +
> > > +static void mtk_uart_apdma_chan_write(struct mtk_chan *c,
> > > +                              unsigned int reg, unsigned int val)
> > > +{
> > > +       writel(val, c->base + reg);
> > > +}
> > > +
> > > +static unsigned int
> > > +mtk_uart_apdma_chan_read(struct mtk_chan *c, unsigned int reg)
> > > +{
> > > +       return readl(c->base + reg);
> > > +}
> > > +
> > > +static void mtk_uart_apdma_desc_free(struct virt_dma_desc *vd)
> > > +{
> > > +       struct dma_chan *chan = vd->tx.chan;
> > > +       struct mtk_chan *c = to_mtk_uart_apdma_chan(chan);
> > > +
> > > +       kfree(c->desc);
> > > +       c->desc = NULL;
> >
> > Why? I'm afraid this may mask double-free.
> >
>
> i will remove it.
>
> > > +}
> > > +
> > > +static void mtk_uart_apdma_start_tx(struct mtk_chan *c)
> > > +{
> > > +       unsigned int txcount = c->desc->avail_len;
> >
> > Variable name is confusing... I'd rather have a boolean `transmitted`
> > (or something), set to 0 here, and set to 1 in the loop (but again,
> > maybe this is not necessary at all, see below).
>
> ok, i modify the function and remove it.
>
> >
> > > +       unsigned int len, send, left, wpt, wrap;
> > > +
> > > +       if (mtk_uart_apdma_chan_read(c, VFF_LEFT_SIZE) == 0U) {
> > > +               mtk_uart_apdma_chan_write(c, VFF_INT_EN, VFF_TX_INT_EN_B);
> >
> > I'd add a "return;" here and de-indent the rest of the function (that
> > should help to make it more readable).
>
> add
>
> >
> > > +       } else {
> > > +               len = mtk_uart_apdma_chan_read(c, VFF_LEN);
> >
> > You make an assumption below that len is always a power of 2. I wonder
> > if we want to validate that with some BUG/WARN call.
> >
> > Also, I assume VFF_LEN is constant? Maybe we can read it once only in
> > the probe function?
> >
>
> no, the value of VFF_LEN isn't constant.
>
> > > +
> > > +               while (((left = mtk_uart_apdma_chan_read(c,
> > > +                                       VFF_LEFT_SIZE)) > 0U)
> > > +                               && (c->desc->avail_len != 0U)) {
> >
> > Why do we need a while loop here? LEFT_SIZE will always be smaller
> > than LEN, right? Shouldn't we load as much as we can, then let an
> > interrupt happen and reload the FIFO at that stage? Or does this help
> > gain a bit of extra performance?
>
> i will remove while, use 'if' instead of.
> >
> > > +                       send = min_t(unsigned int, left, c->desc->avail_len);
> > > +                       wpt = mtk_uart_apdma_chan_read(c, VFF_WPT);
> > > +                       wrap = wpt & MTK_UART_APDMA_RING_WRAP ?
> >
> > wrap = wrp ^ MTK_UART_APDMA_RING_WRAP ?
> >
>
> wrap = wpt & MTK_UART_APDMA_RING_WRAP ?
> i had test it.

Sorry, I got it wrong (and my question mark is confusing), what I mean is this:

wrap = (wrp ^ MTK_UART_APDMA_RING_WRAP) & MTK_UART_APDMA_RING_WRAP;

But then it's marginally shorter than your solution, so maybe keep
yours, it's a little simpler to understand.

> > > +                                       0U : MTK_UART_APDMA_RING_WRAP;
> > > +
> > > +                       if ((wpt & (len - 1U)) + send < len)

Is it possible for wpt > len? If not, then wpt + send < len should be enough.

Also, wpt + send is used a few times now, so maybe have it a separate variable?

Something like this might be nicer:

next_wpt = wpt + send;
if ((wpt & (len - 1U)) + send >= len) {
   next_wpt = next_wpt & (len - 1U);
   if (!(wpt & MTK_UART_APDMA_RING_WRAP))
      next_wpt |= MTK_UART_APDMA_RING_WRAP;
}
mtk_uart_apdma_chan_write(c, VFF_WPT, next_wpt);

Or if the assumption than wpt < len holds:
if (next_wpt >= len) {
   next_wpt = next_wpt - len;
...

> > > +                               mtk_uart_apdma_chan_write(c,
> > > +                                               VFF_WPT, wpt + send);
> > > +                       else
> > > +                               mtk_uart_apdma_chan_write(c, VFF_WPT,
> > > +                                                  ((wpt + send) & (len - 1U))
> > > +                                                  | wrap);
> > > +
> > > +                       c->desc->avail_len -= send;
> > > +               }
> > > +
> > > +               if (txcount != c->desc->avail_len) {
> >
> > We know mtk_uart_apdma_chan_read(c, VFF_LEFT_SIZE) > 0 at least once,
> > so this test should always be true.
> >
> > Unless we have c->desc->avail_len == 0, but then we won't even call
> > this function... So this is always true.
> >
>
> yes. you are right. i will remove it.
>
> > > +                       mtk_uart_apdma_chan_write(c,
> > > +                                       VFF_INT_EN, VFF_TX_INT_EN_B);
> > > +                       if (mtk_uart_apdma_chan_read(c,
> > > +                                               VFF_FLUSH) == 0U)
> > > +                               mtk_uart_apdma_chan_write(c,
> > > +                                               VFF_FLUSH, VFF_FLUSH_B);
> > > +               }
> > > +       }
> > > +}
> > > +
> > > +static void mtk_uart_apdma_start_rx(struct mtk_chan *c)
> > > +{
> > > +       struct mtk_uart_apdma_desc *d = c->desc;
> > > +       unsigned int rx_len, wg, rg, count;
> > > +
> > > +       if (mtk_uart_apdma_chan_read(c, VFF_VALID_SIZE) == 0U)
> > > +               return;
> > > +
> > > +       if (d && vchan_next_desc(&c->vc)) {

I'd negate the test to de-indent the rest of the code:
if (!d || !vchan_next_desc(&c->vc))
   return;

> > > +               rx_len = mtk_uart_apdma_chan_read(c, VFF_LEN);
> > > +               rg = mtk_uart_apdma_chan_read(c, VFF_RPT);
> > > +               wg = mtk_uart_apdma_chan_read(c, VFF_WPT);
> > > +               count = ((rg ^ wg) & MTK_UART_APDMA_RING_WRAP) ?
> > > +                               ((wg & MTK_UART_APDMA_RING_SIZE) +
> > > +                               rx_len - (rg & MTK_UART_APDMA_RING_SIZE)) :
> > > +                               ((wg & MTK_UART_APDMA_RING_SIZE) -
> > > +                               (rg & MTK_UART_APDMA_RING_SIZE));
> >
> > This is hard to read, please use a if/else.
> >
>
> ok.
>
> > > +
> > > +               c->rx_status = count;
> > > +               mtk_uart_apdma_chan_write(c, VFF_RPT, wg);
> > > +
> > > +               list_del(&d->vd.node);
> > > +               vchan_cookie_complete(&d->vd);
> > > +       }
> > > +}
> > > +
> > > +static irqreturn_t mtk_uart_apdma_irq_handler(int irq, void *dev_id)
> > > +{
> > > +       struct dma_chan *chan = (struct dma_chan *)dev_id;
> > > +       struct mtk_chan *c = to_mtk_uart_apdma_chan(chan);
> > > +       struct mtk_uart_apdma_desc *d;
> > > +       unsigned long flags;
> > > +
> > > +       spin_lock_irqsave(&c->vc.lock, flags);
> > > +       switch (c->cfg.direction) {
> > > +       case DMA_DEV_TO_MEM:
> >
> > You use an if/else below in a similar case, please be consistent (IMHO
> > if/else is a bit more compact, so I'd use that here).
> >
> sean wang had review it. the link
> http://lists.infradead.org/pipermail/linux-mediatek/2018-December/016292.html
>
> > > +               mtk_uart_apdma_chan_write(c,
> > > +                               VFF_INT_FLAG, VFF_RX_INT_FLAG_CLR_B);
> > > +               mtk_uart_apdma_start_rx(c);
> > > +               break;
> > > +       case DMA_MEM_TO_DEV:
> > > +               d = c->desc;
> > > +
> > > +               mtk_uart_apdma_chan_write(c,
> > > +                               VFF_INT_FLAG, VFF_TX_INT_FLAG_CLR_B);
> > > +
> > > +               if (d->avail_len != 0U) {
> > > +                       mtk_uart_apdma_start_tx(c);
> > > +               } else {
> > > +                       list_del(&d->vd.node);
> > > +                       vchan_cookie_complete(&d->vd);
> > > +               }
> > > +               break;
> > > +       default:
> > > +               break;
> > > +       }
> > > +       spin_unlock_irqrestore(&c->vc.lock, flags);
> > > +
> > > +       return IRQ_HANDLED;
> > > +}
> > > +
> > > +static int mtk_uart_apdma_alloc_chan_resources(struct dma_chan *chan)
> > > +{
> > > +       struct mtk_uart_apdmadev *mtkd = to_mtk_uart_apdma_dev(chan->device);
> > > +       struct mtk_chan *c = to_mtk_uart_apdma_chan(chan);
> > > +       u32 status;
> > > +       int ret = -EBUSY;

No need to init ret.

> > > +
> > > +       pm_runtime_get_sync(mtkd->ddev.dev);
> > > +
> > > +       mtk_uart_apdma_chan_write(c, VFF_ADDR, 0);
> > > +       mtk_uart_apdma_chan_write(c, VFF_THRE, 0);
> > > +       mtk_uart_apdma_chan_write(c, VFF_LEN, 0);
> > > +       mtk_uart_apdma_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");
> > > +               goto exit;

Just return ret, since you don't do any cleanup in exit:.

> > > +       }
> > > +
> > > +       if (!c->requested) {
> > > +               c->requested = true;
> > > +               ret = request_irq(mtkd->dma_irq[chan->chan_id],
> > > +                                 mtk_uart_apdma_irq_handler,
> > > +                                 IRQF_TRIGGER_NONE,
> > > +                                 KBUILD_MODNAME, chan);
> > > +               if (ret < 0) {
> > > +                       dev_err(chan->device->dev, "Can't request dma IRQ\n");
> > > +                       return -EINVAL;
> > > +               }
> > > +       }
> > > +
> > > +       if (mtkd->support_33bits)
> > > +               mtk_uart_apdma_chan_write(c,
> > > +                               VFF_4G_SUPPORT, VFF_4G_SUPPORT_CLR_B);
> > > +
> > > +exit:
> > > +       return ret;
> > > +}
> > > +
> > > +static void mtk_uart_apdma_free_chan_resources(struct dma_chan *chan)
> > > +{
> > > +       struct mtk_uart_apdmadev *mtkd = to_mtk_uart_apdma_dev(chan->device);
> > > +       struct mtk_chan *c = to_mtk_uart_apdma_chan(chan);
> > > +
> > > +       if (c->requested) {
> > > +               c->requested = false;
> > > +               free_irq(mtkd->dma_irq[chan->chan_id], chan);
> > > +       }
> > > +
> > > +       tasklet_kill(&c->vc.task);
> > > +
> > > +       vchan_free_chan_resources(&c->vc);
> > > +
> > > +       pm_runtime_put_sync(mtkd->ddev.dev);
> > > +}
> > > +
> > > +static enum dma_status mtk_uart_apdma_tx_status(struct dma_chan *chan,
> > > +                                        dma_cookie_t cookie,
> > > +                                        struct dma_tx_state *txstate)
> > > +{
> > > +       struct mtk_chan *c = to_mtk_uart_apdma_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_uart_apdma_chan_read(c, VFF_RPT)
> > > +                            & MTK_UART_APDMA_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;
> > > +}
> > > +
> > > +/*
> > > + * dmaengine_prep_slave_single will call the function. and sglen is 1.
> > > + * 8250 uart using one ring buffer, and deal with one sg.
> > > + */
> > > +static struct dma_async_tx_descriptor *mtk_uart_apdma_prep_slave_sg
> > > +       (struct dma_chan *chan, struct scatterlist *sgl,
> > > +       unsigned int sglen,     enum dma_transfer_direction dir,

Too many spaces (or a tab?) between `sglen,` and `enum`

> > > +       unsigned long tx_flags, void *context)
> > > +{
> > > +       struct mtk_chan *c = to_mtk_uart_apdma_chan(chan);
> > > +       struct mtk_uart_apdma_desc *d;
> > > +
> > > +       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), GFP_ATOMIC);
> > > +       if (!d)
> > > +               return NULL;
> > > +
> > > +       /* sglen is 1 */
> > > +       d->avail_len = sg_dma_len(sgl);
> > > +
> > > +       return vchan_tx_prep(&c->vc, &d->vd, tx_flags);
> > > +}
> > > +
> > > +static void mtk_uart_apdma_issue_pending(struct dma_chan *chan)
> > > +{
> > > +       struct mtk_chan *c = to_mtk_uart_apdma_chan(chan);
> > > +       struct virt_dma_desc *vd;
> > > +       unsigned long flags;
> > > +
> > > +       spin_lock_irqsave(&c->vc.lock, flags);
> > > +       if (c->cfg.direction == DMA_DEV_TO_MEM) {
> > > +               if (vchan_issue_pending(&c->vc) && !c->desc) {
> > > +                       vd = vchan_next_desc(&c->vc);
> > > +                       c->desc = to_mtk_uart_apdma_desc(&vd->tx);
> > > +                       mtk_uart_apdma_start_rx(c);
> > > +               }
> > > +       } 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_uart_apdma_desc(&vd->tx);
> > > +                       mtk_uart_apdma_start_tx(c);
> > > +               }
> > > +       }
> > > +       spin_unlock_irqrestore(&c->vc.lock, flags);
> > > +}
> > > +
> > > +static int mtk_uart_apdma_slave_config(struct dma_chan *chan,
> > > +                               struct dma_slave_config *cfg)
> > > +{
> > > +       struct mtk_chan *c = to_mtk_uart_apdma_chan(chan);
> > > +       struct mtk_uart_apdmadev *mtkd =
> > > +                               to_mtk_uart_apdma_dev(c->vc.chan.device);
> > > +
> > > +       c->cfg = *cfg;
> > > +
> > > +       if (cfg->direction == DMA_DEV_TO_MEM) {
> > > +               unsigned int rx_len = cfg->src_addr_width * 1024;
> > > +
> > > +               mtk_uart_apdma_chan_write(c, VFF_ADDR, cfg->src_addr);
> > > +               mtk_uart_apdma_chan_write(c, VFF_LEN, rx_len);
> > > +               mtk_uart_apdma_chan_write(c, VFF_THRE, VFF_RX_THRE(rx_len));
> > > +               mtk_uart_apdma_chan_write(c,
> > > +                               VFF_INT_EN, VFF_RX_INT_EN0_B
> > > +                               | VFF_RX_INT_EN1_B);
> > > +               mtk_uart_apdma_chan_write(c, VFF_RPT, 0);
> > > +               mtk_uart_apdma_chan_write(c,
> > > +                               VFF_INT_FLAG, VFF_RX_INT_FLAG_CLR_B);
> > > +               mtk_uart_apdma_chan_write(c, VFF_EN, VFF_EN_B);
> > > +       } else if (cfg->direction == DMA_MEM_TO_DEV)    {
> > > +               unsigned int tx_len = cfg->dst_addr_width * 1024;
> > > +
> > > +               mtk_uart_apdma_chan_write(c, VFF_ADDR, cfg->dst_addr);
> > > +               mtk_uart_apdma_chan_write(c, VFF_LEN, tx_len);
> > > +               mtk_uart_apdma_chan_write(c, VFF_THRE, VFF_TX_THRE(tx_len));
> > > +               mtk_uart_apdma_chan_write(c, VFF_WPT, 0);
> > > +               mtk_uart_apdma_chan_write(c,
> > > +                               VFF_INT_FLAG, VFF_TX_INT_FLAG_CLR_B);
> > > +               mtk_uart_apdma_chan_write(c, VFF_EN, VFF_EN_B);
> > > +       }
> > > +
> > > +       if (mtkd->support_33bits)
> > > +               mtk_uart_apdma_chan_write(c, VFF_4G_SUPPORT, VFF_4G_SUPPORT_B);
> > > +
> > > +       if (mtk_uart_apdma_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_uart_apdma_terminate_all(struct dma_chan *chan)
> > > +{
> > > +       struct mtk_chan *c = to_mtk_uart_apdma_chan(chan);
> > > +       unsigned long flags;
> > > +       u32 status;
> > > +       int ret;
> > > +
> > > +       spin_lock_irqsave(&c->vc.lock, flags);
> > > +
> > > +       mtk_uart_apdma_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_uart_apdma_chan_read(c, VFF_DEBUG_STATUS));
> > > +
> > > +       /*set stop as 1 -> wait until en is 0 -> set stop as 0*/
> > > +       mtk_uart_apdma_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_uart_apdma_chan_read(c, VFF_DEBUG_STATUS));
> > > +
> > > +       mtk_uart_apdma_chan_write(c, VFF_STOP, VFF_STOP_CLR_B);
> > > +       mtk_uart_apdma_chan_write(c, VFF_INT_EN, VFF_INT_EN_CLR_B);
> > > +
> > > +       switch (c->cfg.direction) {
> > > +       case DMA_DEV_TO_MEM:
> >
> > Ditto, if/else?
> >
> ditto.
> http://lists.infradead.org/pipermail/linux-mediatek/2018-December/016292.html

Well, I disagree, especially in this case: We turn 4 lines of code into 10...

> > > +               mtk_uart_apdma_chan_write(c,
> > > +                               VFF_INT_FLAG, VFF_RX_INT_FLAG_CLR_B);
> > > +               break;
> > > +       case DMA_MEM_TO_DEV:
> > > +               mtk_uart_apdma_chan_write(c,
> > > +                               VFF_INT_FLAG, VFF_TX_INT_FLAG_CLR_B);
> > > +               break;
> > > +       default:
> > > +               break;
> > > +       }
> > > +
> > > +       spin_unlock_irqrestore(&c->vc.lock, flags);
> > > +
> > > +       return 0;
> > > +}
> > > +
> > > +static int mtk_uart_apdma_device_pause(struct dma_chan *chan)
> > > +{
> > > +       /* just for check caps pass */
> > > +       return 0;
> > > +}
> > > +
> > > +static int mtk_uart_apdma_device_resume(struct dma_chan *chan)
> > > +{
> > > +       /* just for check caps pass */
> > > +       return 0;
> > > +}

Why do you need these? Seems wrong to advertise device_pause/resume
(and the caps) if we don't actually support that?

> > > +
> > > +static void mtk_uart_apdma_free(struct mtk_uart_apdmadev *mtkd)
> > > +{
> > > +       while (list_empty(&mtkd->ddev.channels) == 0) {
> > > +               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);
> > > +       }
> > > +}
> > > +
> > > +static const struct of_device_id mtk_uart_apdma_match[] = {
> > > +       { .compatible = "mediatek,mt6577-uart-dma", },
> > > +       { /* sentinel */ },
> > > +};
> > > +MODULE_DEVICE_TABLE(of, mtk_uart_apdma_match);
> > > +
> > > +static int mtk_uart_apdma_probe(struct platform_device *pdev)
> > > +{
> > > +       struct mtk_uart_apdmadev *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;
> > > +
> > > +       mtkd->clk = devm_clk_get(&pdev->dev, NULL);
> > > +       if (IS_ERR(mtkd->clk)) {
> > > +               dev_err(&pdev->dev, "No clock specified\n");
> > > +               rc = PTR_ERR(mtkd->clk);
> > > +               goto err_no_dma;
> > > +       }
> > > +
> > > +       if (of_property_read_bool(pdev->dev.of_node, "dma-33bits")) {
> > > +               dev_info(&pdev->dev, "Support dma 33bits\n");
> >
> > Drop this, a bit verbose.
> >
> > > +               mtkd->support_33bits = true;
> > > +       }
> > > +
> > > +       rc = dma_set_mask_and_coherent(&pdev->dev,
> > > +                               DMA_BIT_MASK(32 | mtkd->support_33bits));
> > > +       if (rc)
> > > +               goto err_no_dma;
> > > +
> > > +       dma_cap_set(DMA_SLAVE, mtkd->ddev.cap_mask);
> > > +       mtkd->ddev.device_alloc_chan_resources =
> > > +                               mtk_uart_apdma_alloc_chan_resources;
> > > +       mtkd->ddev.device_free_chan_resources =
> > > +                               mtk_uart_apdma_free_chan_resources;
> > > +       mtkd->ddev.device_tx_status = mtk_uart_apdma_tx_status;
> > > +       mtkd->ddev.device_issue_pending = mtk_uart_apdma_issue_pending;
> > > +       mtkd->ddev.device_prep_slave_sg = mtk_uart_apdma_prep_slave_sg;
> > > +       mtkd->ddev.device_config = mtk_uart_apdma_slave_config;
> > > +       mtkd->ddev.device_pause = mtk_uart_apdma_device_pause;
> > > +       mtkd->ddev.device_resume = mtk_uart_apdma_device_resume;
> > > +       mtkd->ddev.device_terminate_all = mtk_uart_apdma_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);
> > > +
> > > +       for (i = 0; i < MTK_UART_APDMA_CHANNELS; i++) {
> > > +               c = devm_kzalloc(mtkd->ddev.dev, sizeof(*c), GFP_KERNEL);
> > > +               if (!c) {
> > > +                       rc = -ENODEV;
> > > +                       goto err_no_dma;
> > > +               }
> > > +
> > > +               res = platform_get_resource(pdev, IORESOURCE_MEM, i);
> > > +               if (!res) {
> > > +                       rc = -ENODEV;
> > > +                       goto err_no_dma;
> > > +               }
> > > +
> > > +               c->base = devm_ioremap_resource(&pdev->dev, res);
> > > +               if (IS_ERR(c->base)) {
> > > +                       rc = PTR_ERR(c->base);
> > > +                       goto err_no_dma;
> > > +               }
> > > +               c->requested = false;
> > > +               c->vc.desc_free = mtk_uart_apdma_desc_free;
> > > +               vchan_init(&c->vc, &mtkd->ddev);
> > > +
> > > +               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);
> > > +                       rc = -EINVAL;
> > > +                       goto err_no_dma;
> > > +               }
> > > +       }
> > > +
> > > +       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_uart_apdma_free(mtkd);

It's not very correct to call this before
INIT_LIST_HEAD(&mtkd->ddev.channels);

I'd just call `return rc;` directly for all instances before that line.

> > > +       return rc;
> > > +}
> > > +
> > > +static int mtk_uart_apdma_remove(struct platform_device *pdev)
> > > +{
> > > +       struct mtk_uart_apdmadev *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_uart_apdma_free(mtkd);
> > > +
> > > +       return 0;
> > > +}
> > > +
> > > +#ifdef CONFIG_PM_SLEEP
> > > +static int mtk_uart_apdma_suspend(struct device *dev)
> > > +{
> > > +       struct mtk_uart_apdmadev *mtkd = dev_get_drvdata(dev);
> > > +
> > > +       if (!pm_runtime_suspended(dev))
> > > +               clk_disable_unprepare(mtkd->clk);
> > > +
> > > +       return 0;
> > > +}
> > > +
> > > +static int mtk_uart_apdma_resume(struct device *dev)
> > > +{
> > > +       int ret;
> > > +       struct mtk_uart_apdmadev *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_uart_apdma_runtime_suspend(struct device *dev)
> > > +{
> > > +       struct mtk_uart_apdmadev *mtkd = dev_get_drvdata(dev);
> > > +
> > > +       clk_disable_unprepare(mtkd->clk);
> > > +
> > > +       return 0;
> > > +}
> > > +
> > > +static int mtk_uart_apdma_runtime_resume(struct device *dev)
> > > +{
> > > +       int ret;
> > > +       struct mtk_uart_apdmadev *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_uart_apdma_pm_ops = {
> > > +       SET_SYSTEM_SLEEP_PM_OPS(mtk_uart_apdma_suspend, mtk_uart_apdma_resume)
> > > +       SET_RUNTIME_PM_OPS(mtk_uart_apdma_runtime_suspend,
> > > +                          mtk_uart_apdma_runtime_resume, NULL)
> > > +};
> > > +
> > > +static struct platform_driver mtk_uart_apdma_driver = {
> > > +       .probe  = mtk_uart_apdma_probe,
> > > +       .remove = mtk_uart_apdma_remove,
> > > +       .driver = {
> > > +               .name           = KBUILD_MODNAME,
> > > +               .pm             = &mtk_uart_apdma_pm_ops,
> > > +               .of_match_table = of_match_ptr(mtk_uart_apdma_match),
> > > +       },
> > > +};
> > > +
> > > +module_platform_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..1a523c87 100644
> > > --- a/drivers/dma/mediatek/Kconfig
> > > +++ b/drivers/dma/mediatek/Kconfig
> > > @@ -1,4 +1,15 @@
> > >
> > > +config DMA_MTK_UART
> > > +       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 SERIAL_8250_MT6577 is enabled, and if you want to use DMA,
> > > +         you can enable the config. the DMA engine can only be used
> > > +         with MediaTek 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_HSDMA) += mtk-hsdma.o
> > > --
> > > 1.7.9.5
> > >
>
>