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Date:	Wed, 24 Dec 2014 20:06:25 +0000
From:	James Hartley <James.Hartley@...tec.com>
To:	Andrew Bresticker <abrestic@...omium.org>
CC:	Vinod Koul <vinod.koul@...el.com>,
	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 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" <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 24 Dec 2014, at 17:21, Andrew Bresticker <abrestic@...omium.org> wrote:
> 
>> 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.

Pause / resume is not supported by the MDC hardware. 

James. --
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