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Date:	Wed, 24 Dec 2014 09:21:11 -0800
From:	Andrew Bresticker <abrestic@...omium.org>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	Dan Williams <dan.j.williams@...el.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Grant Likely <grant.likely@...aro.org>,
	James Hartley <james.hartley@...tec.com>,
	James Hogan <james.hogan@...tec.com>,
	Ezequiel Garcia <ezequiel.garcia@...tec.com>,
	Damien Horsley <Damien.Horsley@...tec.com>,
	Arnd Bergmann <arnd@...db.de>, dmaengine@...r.kernel.org,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V3 2/2] dmaengine: Add driver for IMG MDC

On Tue, Dec 23, 2014 at 9:22 PM, Vinod Koul <vinod.koul@...el.com> wrote:
> On Thu, Dec 11, 2014 at 02:59:17PM -0800, Andrew Bresticker wrote:
>> Add support for the IMG Multi-threaded DMA Controller (MDC) found on
>> certain IMG SoCs.  Currently this driver supports the variant present
>> on the MIPS-based Pistachio SoC.a

> Overall looks okay. I also need some review by DT folks on the bindings

Arnd has ack'ed the DT bindings, do you need someone else to review
them as well?

>> +static void mdc_list_desc_config(struct mdc_chan *mchan,
>> +                              struct mdc_hw_list_desc *ldesc,
>> +                              enum dma_transfer_direction dir,
>> +                              dma_addr_t src, dma_addr_t dst, size_t len)
>> +{
>> +     struct mdc_dma *mdma = mchan->mdma;
>> +     unsigned int max_burst, burst_size;
>> +
>> +     ldesc->gen_conf = MDC_GENERAL_CONFIG_IEN | MDC_GENERAL_CONFIG_LIST_IEN |
>> +             MDC_GENERAL_CONFIG_LEVEL_INT | MDC_GENERAL_CONFIG_PHYSICAL_W |
>> +             MDC_GENERAL_CONFIG_PHYSICAL_R;
>> +     ldesc->readport_conf =
>> +             (mchan->thread << MDC_READ_PORT_CONFIG_STHREAD_SHIFT) |
>> +             (mchan->thread << MDC_READ_PORT_CONFIG_RTHREAD_SHIFT) |
>> +             (mchan->thread << MDC_READ_PORT_CONFIG_WTHREAD_SHIFT);
>> +     ldesc->read_addr = src;
>> +     ldesc->write_addr = dst;
>> +     ldesc->xfer_size = len - 1;
>> +     ldesc->node_addr = 0;
>> +     ldesc->cmds_done = 0;
>> +     ldesc->ctrl_status = MDC_CONTROL_AND_STATUS_LIST_EN |
>> +             MDC_CONTROL_AND_STATUS_EN;
>> +     ldesc->next_desc = NULL;
>> +
>> +     if (IS_ALIGNED(dst, mdma->bus_width) &&
>> +         IS_ALIGNED(src, mdma->bus_width))
>> +             max_burst = mdma->bus_width * mdma->max_burst_mult;
>> +     else
>> +             max_burst = mdma->bus_width * (mdma->max_burst_mult - 1);
>> +
>> +     if (dir == DMA_MEM_TO_DEV) {
>> +             ldesc->gen_conf |= MDC_GENERAL_CONFIG_INC_R;
>> +             ldesc->readport_conf |= MDC_READ_PORT_CONFIG_DREQ_ENABLE;
>> +             mdc_set_read_width(ldesc, mdma->bus_width);
>> +             mdc_set_write_width(ldesc, mchan->config.dst_addr_width);
>> +             burst_size = min(max_burst, mchan->config.dst_maxburst *
>> +                              mchan->config.dst_addr_width);

> why is this calculation done for burst size? Shouldn't we take the
> config.dst_maxburst value configured by client?

It's possible that the client could select a burst size that is too
large (i.e. it exceeds the max_burst calculated above), so we cap it
here to max_burst.

>> +static struct dma_async_tx_descriptor *mdc_prep_slave_sg(
>> +     struct dma_chan *chan, struct scatterlist *sgl,
>> +     unsigned int sg_len, enum dma_transfer_direction dir,
>> +     unsigned long flags, void *context)
>> +{
>> +     struct mdc_chan *mchan = to_mdc_chan(chan);
>> +     struct mdc_dma *mdma = mchan->mdma;
>> +     struct mdc_tx_desc *mdesc;
>> +     struct scatterlist *sg;
>> +     struct mdc_hw_list_desc *curr, *prev = NULL;
>> +     dma_addr_t curr_phys, prev_phys;
>> +     unsigned int i;
>> +
>> +     if (!sgl)
>> +             return NULL;
>> +
>> +     if (!is_slave_direction(dir))
>> +             return NULL;
>> +
>> +     if (mdc_check_slave_width(mchan, dir) < 0)
>> +             return NULL;
>> +
>> +     mdesc = kzalloc(sizeof(*mdesc), GFP_NOWAIT);
>> +     if (!mdesc)
>> +             return NULL;
>> +     mdesc->chan = mchan;
>> +
>> +     for_each_sg(sgl, sg, sg_len, i) {
>> +             dma_addr_t buf = sg_dma_address(sg);
>> +             size_t buf_len = sg_dma_len(sg);
>> +
>> +             while (buf_len > 0) {
>> +                     size_t xfer_size;
>> +
>> +                     curr = dma_pool_alloc(mdma->desc_pool, GFP_NOWAIT,
>> +                                           &curr_phys);
>> +                     if (!curr)
>> +                             goto free_desc;
>> +
>> +                     if (!prev) {
>> +                             mdesc->list_phys = curr_phys;
>> +                             mdesc->list = curr;
>> +                     } else {
>> +                             prev->node_addr = curr_phys;
>> +                             prev->next_desc = curr;
>> +                     }
>> +
>> +                     xfer_size = min_t(size_t, mdma->max_xfer_size,
>> +                                       buf_len);
>> +
>> +                     if (dir == DMA_MEM_TO_DEV) {
>> +                             mdc_list_desc_config(mchan, curr, dir, buf,
>> +                                                  mchan->config.dst_addr,
>> +                                                  xfer_size);
>> +                     } else {
>> +                             mdc_list_desc_config(mchan, curr, dir,
>> +                                                  mchan->config.src_addr,
>> +                                                  buf, xfer_size);
>> +                     }
>> +
>> +                     prev = curr;
>> +                     prev_phys = curr_phys;
>> +
>> +                     mdesc->list_len++;
>> +                     mdesc->list_xfer_size += xfer_size;
>> +                     buf += xfer_size;
>> +                     buf_len -= xfer_size;

> i see this pattern is repeat in all the .prepare calls, can we make it bit
> generic and use that in the these three calls..

I've pulled out almost all of the common stuff into
mdc_list_desc_config().  I suppose the list manipulation could be
moved there as well, but the rest is all slightly different in each
case.

>> +     dma_cap_zero(mdma->dma_dev.cap_mask);
>> +     dma_cap_set(DMA_SLAVE, mdma->dma_dev.cap_mask);
>> +     dma_cap_set(DMA_PRIVATE, mdma->dma_dev.cap_mask);
>> +     dma_cap_set(DMA_CYCLIC, mdma->dma_dev.cap_mask);

> and you dont seen to support pause/resume, though not a blocker but is it
> not supported in HW or driver doesn't?

Someone from IMG can correct me if I'm wrong, but I don't think the HW
supports it.
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