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Date:   Thu, 17 May 2018 11:41:35 +0530
From:   Vinod <vkoul@kernel.org>
To:     Baolin Wang <baolin.wang@linaro.org>
Cc:     Dan Williams <dan.j.williams@intel.com>,
        Eric Long <eric.long@spreadtrum.com>,
        Mark Brown <broonie@kernel.org>, dmaengine@vger.kernel.org,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v3 2/2] dmaengine: sprd: Add Spreadtrum DMA configuration
Message-ID: <20180517061135.GV13271@vkoul-mobl>
References: <08819489e52add194fecf2b4b234fff9deecdb4c.1526043689.git.baolin.wang@linaro.org>
 <85413038c111c58747194dd5736834be9adb0f20.1526043689.git.baolin.wang@linaro.org>
 <20180517051447.GS13271@vkoul-mobl>
 <CAMz4kuKtfwRfm4zcSYFrr=FHQzQSBYUD2ZSYuzgJ41sjPyBUmQ@mail.gmail.com>
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On 17-05-18, 14:02, Baolin Wang wrote:
> Hi Vinod,
> 
> On 17 May 2018 at 13:14, Vinod <vkoul@kernel.org> wrote:
> > On 11-05-18, 21:06, Baolin Wang wrote:
> >> +struct sprd_dma_config {
> >> +     struct dma_slave_config cfg;
> >> +     u32 block_len;
> >> +     u32 transcation_len;
> >
> > /s/transcation/transaction
> 
> OK.
> 
> >
> > now in code I see block_len and this filled by len which is sg_dma_len()?
> > So why two varibales when you are using only one.
> 
> Like I explained before, we have transaction transfer, block transfer
> and fragment transfer, and we should set the length for each transfer.
> In future, we we will use these two variables in cyclic mode, but for
> prep_sg, we just make them equal to

Please add them when you have use for it. Sorry linux kernel is not a place for
dumping future use work

> 
> >
> > Second, you are storing parameters programmed thru _prep call into
> > _dma_config. That is not correct.
> >
> > We use these to store channel parameters and NOT transaction parameters which
> > would differ with each txn. No wonder you can only support only 1 txn :)
> 
> Fine, we can remove block_len/transcation_len from 'struct
> sprd_dma_config'. Any other issues for the 'struct sprd_dma_config'?

Yes see the comments on prep_

> 
> >
> > Lastly, if these are same values why not use src/dstn_max_burst?
> 
> The fragment length will be filled by src/dstn_max_burst,so we can not
> use it again.
> 
> >
> >> +static enum sprd_dma_datawidth
> >> +sprd_dma_get_datawidth(enum dma_slave_buswidth buswidth)
> >> +{
> >> +     switch (buswidth) {
> >> +     case DMA_SLAVE_BUSWIDTH_1_BYTE:
> >> +     case DMA_SLAVE_BUSWIDTH_2_BYTES:
> >> +     case DMA_SLAVE_BUSWIDTH_4_BYTES:
> >> +     case DMA_SLAVE_BUSWIDTH_8_BYTES:
> >> +             return ffs(buswidth) - 1;
> >> +     default:
> >> +             return SPRD_DMA_DATAWIDTH_4_BYTES;
> >
> > Does default make sense, should we error out?
> 
> Not one error, maybe we can give some warning information.

well client programmed a wrong value, so I expect this to error out.

> 
> >
> >> +static u32 sprd_dma_get_step(enum dma_slave_buswidth buswidth)
> >> +{
> >> +     switch (buswidth) {
> >> +     case DMA_SLAVE_BUSWIDTH_1_BYTE:
> >> +     case DMA_SLAVE_BUSWIDTH_2_BYTES:
> >> +     case DMA_SLAVE_BUSWIDTH_4_BYTES:
> >> +     case DMA_SLAVE_BUSWIDTH_8_BYTES:
> >> +             return buswidth;
> >> +
> >> +     default:
> >> +             return SPRD_DMA_DWORD_STEP;
> >
> > Does default make sense, should we error out?
> 
> Ditto.
> 
> >
> >> +static int sprd_dma_config(struct dma_chan *chan, struct sprd_dma_desc *sdesc,
> >> +                        dma_addr_t src, dma_addr_t dst,
> >> +                        struct sprd_dma_config *slave_cfg)
> >> +{
> >> +     struct sprd_dma_dev *sdev = to_sprd_dma_dev(chan);
> >> +     struct sprd_dma_chn *schan = to_sprd_dma_chan(chan);
> >> +     struct sprd_dma_chn_hw *hw = &sdesc->chn_hw;
> >> +     u32 fix_mode = 0, fix_en = 0, wrap_en = 0, wrap_mode = 0;
> >> +     u32 src_datawidth, dst_datawidth, temp;
> >> +
> >> +     if (slave_cfg->cfg.slave_id)
> >> +             schan->dev_id = slave_cfg->cfg.slave_id;
> >> +
> >> +     hw->cfg = SPRD_DMA_DONOT_WAIT_BDONE << SPRD_DMA_WAIT_BDONE_OFFSET;
> >> +
> >> +     temp = slave_cfg->wrap_ptr & SPRD_DMA_LOW_ADDR_MASK;
> >> +     temp |= (src >> SPRD_DMA_HIGH_ADDR_OFFSET) & SPRD_DMA_HIGH_ADDR_MASK;
> >> +     hw->wrap_ptr = temp;
> >> +
> >> +     temp = slave_cfg->wrap_to & SPRD_DMA_LOW_ADDR_MASK;
> >> +     temp |= (dst >> SPRD_DMA_HIGH_ADDR_OFFSET) & SPRD_DMA_HIGH_ADDR_MASK;
> >> +     hw->wrap_to = temp;
> >> +
> >> +     hw->src_addr = src & SPRD_DMA_LOW_ADDR_MASK;
> >> +     hw->des_addr = dst & SPRD_DMA_LOW_ADDR_MASK;
> >> +
> >> +     if ((slave_cfg->src_step != 0 && slave_cfg->dst_step != 0)
> >> +         || (slave_cfg->src_step | slave_cfg->dst_step) == 0) {
> >
> > this check doesnt seem right to me, what are you trying here?
> 
> This is SPRD DMA internal feature: address-fix transfer. If the src
> step and dst step both are 0 or both are not 0, that means we can not
> enable the fix mode.
> If one is 0 and another one is not, we can enable the fix mode.

A comment here would help explain this :)

> 
> >
> >> +             fix_en = 0;
> >> +     } else {
> >> +             fix_en = 1;
> >> +             if (slave_cfg->src_step)
> >> +                     fix_mode = 1;
> >> +             else
> >> +                     fix_mode = 0;
> >> +     }
> >> +
> >> +     if (slave_cfg->wrap_ptr && slave_cfg->wrap_to) {
> >> +             wrap_en = 1;
> >> +             if (slave_cfg->wrap_to == src) {
> >> +                     wrap_mode = 0;
> >> +             } else if (slave_cfg->wrap_to == dst) {
> >> +                     wrap_mode = 1;
> >> +             } else {
> >> +                     dev_err(sdev->dma_dev.dev, "invalid wrap mode\n");
> >> +                     return -EINVAL;
> >> +             }
> >> +     }
> >> +
> >> +     hw->intc = slave_cfg->int_mode | SPRD_DMA_CFG_ERR_INT_EN;
> >> +
> >> +     src_datawidth = sprd_dma_get_datawidth(slave_cfg->cfg.src_addr_width);
> >> +     dst_datawidth = sprd_dma_get_datawidth(slave_cfg->cfg.dst_addr_width);
> >> +
> >> +     temp = src_datawidth << SPRD_DMA_SRC_DATAWIDTH_OFFSET;
> >> +     temp |= dst_datawidth << SPRD_DMA_DES_DATAWIDTH_OFFSET;
> >> +     temp |= slave_cfg->req_mode << SPRD_DMA_REQ_MODE_OFFSET;
> >> +     temp |= wrap_mode << SPRD_DMA_WRAP_SEL_OFFSET;
> >> +     temp |= wrap_en << SPRD_DMA_WRAP_EN_OFFSET;
> >> +     temp |= fix_mode << SPRD_DMA_FIX_SEL_OFFSET;
> >> +     temp |= fix_en << SPRD_DMA_FIX_EN_OFFSET;
> >> +     temp |= slave_cfg->cfg.src_maxburst & SPRD_DMA_FRG_LEN_MASK;
> >> +     hw->frg_len = temp;
> >> +
> >> +     hw->blk_len = slave_cfg->block_len & SPRD_DMA_BLK_LEN_MASK;
> >> +     hw->trsc_len = slave_cfg->transcation_len & SPRD_DMA_TRSC_LEN_MASK;
> >> +
> >> +     temp = (slave_cfg->dst_step & SPRD_DMA_TRSF_STEP_MASK) <<
> >> +             SPRD_DMA_DEST_TRSF_STEP_OFFSET;
> >> +     temp |= (slave_cfg->src_step & SPRD_DMA_TRSF_STEP_MASK) <<
> >> +             SPRD_DMA_SRC_TRSF_STEP_OFFSET;
> >> +     hw->trsf_step = temp;
> >> +
> >> +     hw->frg_step = 0;
> >> +     hw->src_blk_step = 0;
> >> +     hw->des_blk_step = 0;
> >> +     return 0;
> >> +}
> >> +static struct dma_async_tx_descriptor *
> >> +sprd_dma_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
> >> +                    unsigned int sglen, enum dma_transfer_direction dir,
> >> +                    unsigned long flags, void *context)
> >> +{
> >> +     struct sprd_dma_chn *schan = to_sprd_dma_chan(chan);
> >> +     struct sprd_dma_config *slave_cfg = &schan->slave_cfg;
> >> +     u32 src_step = 0, dst_step = 0, len = 0;
> >> +     dma_addr_t src = 0, dst = 0;
> >> +     struct sprd_dma_desc *sdesc;
> >> +     struct scatterlist *sg;
> >> +     int ret, i;
> >> +
> >> +     /* TODO: now we only support one sg for each DMA configuration. */
> >> +     if (!is_slave_direction(dir) || sglen > 1)
> >> +             return NULL;
> >> +
> >> +     sdesc = kzalloc(sizeof(*sdesc), GFP_NOWAIT);
> >> +     if (!sdesc)
> >> +             return NULL;
> >> +
> >> +     for_each_sg(sgl, sg, sglen, i) {
> >> +             len = sg_dma_len(sg);
> >> +
> >> +             if (dir == DMA_MEM_TO_DEV) {
> >> +                     src = sg_dma_address(sg);
> >> +                     dst = slave_cfg->cfg.dst_addr;
> >> +                     src_step = sprd_dma_get_step(slave_cfg->cfg.src_addr_width);
> >> +                     dst_step = SPRD_DMA_NONE_STEP;
> >> +             } else {
> >> +                     src = slave_cfg->cfg.src_addr;
> >> +                     dst = sg_dma_address(sg);
> >> +                     src_step = SPRD_DMA_NONE_STEP;
> >> +                     dst_step = sprd_dma_get_step(slave_cfg->cfg.dst_addr_width);
> >> +             }
> >> +     }
> >> +
> >> +     sprd_dma_fill_config(slave_cfg, src_step, dst_step, len, flags);
> >> +
> >> +     ret = sprd_dma_config(chan, sdesc, src, dst, slave_cfg);
> >> +     if (ret) {
> >> +             kfree(sdesc);
> >> +             return NULL;
> >> +     }
> >
> > Am more intrigued here, the above call fills you config struct but you do not
> > use it.. so what is the use of that.
> 
> I did not get you here. We have passed the slave_cfg to
> sprd_dma_config() to configure DMA hardware channel. Thanks.

But you are not using that... So why bother configuring!

Again this is a channel specific data structure and not transaction specific.
The values should go into descriptor and not something which is channel specific

-- 
~Vinod