Re: [PATCH 01/14] dma: sun6i-dma: Add burst case of 4

From: Chen-Yu Tsai
Date: Sat Oct 29 2016 - 22:08:42 EST

Hi,

On Fri, Oct 28, 2016 at 1:51 AM, Maxime Ripard
<maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote:
> On Sun, Oct 23, 2016 at 06:31:07PM +0200, Jean-Francois Moine wrote:
>> On Tue, 4 Oct 2016 18:55:54 +0200
>> Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx> wrote:
>>
>> > On Tue, Oct 04, 2016 at 12:40:11PM +0200, Jean-Francois Moine wrote:
>> > > On Tue, 4 Oct 2016 11:46:14 +0200
>> > > MylÃne Josserand <mylene.josserand@xxxxxxxxxxxxxxxxxx> wrote:
>> > >
>> > > > Add the case of a burst of 4 which is handled by the SoC.
>> > > >
>> > > > Signed-off-by: MylÃne Josserand <mylene.josserand@xxxxxxxxxxxxxxxxxx>
>> > > > ---
>> > > > drivers/dma/sun6i-dma.c | 2 ++
>> > > > 1 file changed, 2 insertions(+)
>> > > >
>> > > > diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
>> > > > index 8346199..0485204 100644
>> > > > --- a/drivers/dma/sun6i-dma.c
>> > > > +++ b/drivers/dma/sun6i-dma.c
>> > > > @@ -240,6 +240,8 @@ static inline s8 convert_burst(u32 maxburst)
>> > > > switch (maxburst) {
>> > > > case 1:
>> > > > return 0;
>> > > > + case 4:
>> > > > + return 1;
>> > > > case 8:
>> > > > return 2;
>> > > > default:
>> > > > --
>> > > > 2.9.3
>> > >
>> > > This patch has already been rejected by Maxime in the threads
>> > > http://www.spinics.net/lists/dmaengine/msg08610.html
>> > > and
>> > > http://www.spinics.net/lists/dmaengine/msg08719.html
>> > >
>> > > I hope you will find the way he wants for this maxburst to be added.
>> >
>> > I was talking about something along these lines (not tested):
>>
>> I wonder why you don't submit this yourself.
>
> I thought you were the one who cared. You asked for what I had in
> mind, here it is.
>
>> > -------8<---------
>> > diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
>> > index 83461994e418..573ac4608293 100644
>> > --- a/drivers/dma/sun6i-dma.c
>> > +++ b/drivers/dma/sun6i-dma.c
>> > @@ -240,6 +240,8 @@ static inline s8 convert_burst(u32 maxburst)
>> > switch (maxburst) {
>> > case 1:
>> > return 0;
>> > + case 4:
>> > + return 1;
>> > case 8:
>> > return 2;
>> > default:
>> > @@ -1110,11 +1112,19 @@ static int sun6i_dma_probe(struct platform_device *pdev)
>> > sdc->slave.dst_addr_widths = BIT(DMA_SLAVE_BUSWIDTH_1_BYTE) |
>> > BIT(DMA_SLAVE_BUSWIDTH_2_BYTES) |
>> > BIT(DMA_SLAVE_BUSWIDTH_4_BYTES);
>> > + sdc->slave.dst_bursts = BIT(1) | BIT(8);
>> > + sdc->slave.src_bursts = BIT(1) | BIT(8);
>> > sdc->slave.directions = BIT(DMA_DEV_TO_MEM) |
>> > BIT(DMA_MEM_TO_DEV);
>> > sdc->slave.residue_granularity = DMA_RESIDUE_GRANULARITY_BURST;
>> > sdc->slave.dev = &pdev->dev;
>> >
>> > + if (of_device_is_compatible(pdev->dev.of_node,
>> > + "allwinner,sun8i-h3-dma")) {
>> > + sdc->slave.dst_bursts |= BIT(4);
>> > + sdc->slave.src_bursts |= BIT(4);
>> > + }
>> > +
>> > sdc->pchans = devm_kcalloc(&pdev->dev, sdc->cfg->nr_max_channels,
>> > sizeof(struct sun6i_pchan), GFP_KERNEL);
>> > if (!sdc->pchans)
>> > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
>> > index cc535a478bae..f7bbec24bb58 100644
>> > --- a/include/linux/dmaengine.h
>> > +++ b/include/linux/dmaengine.h
>> > @@ -673,6 +673,8 @@ struct dma_filter {
>> > * each type of direction, the dma controller should fill (1 <<
>> > * <TYPE>) and same should be checked by controller as well
>> > * @max_burst: max burst capability per-transfer
>> > + * @dst_bursts: bitfield of the available burst sizes for the destination
>> > + * @src_bursts: bitfield of the available burst sizes for the source
>>
>> You did not define dst_bursts nor src_bursts.
>>
>> > * @residue_granularity: granularity of the transfer residue reported
>> > * by tx_status
>> > * @device_alloc_chan_resources: allocate resources and return the
>> > @@ -800,6 +802,14 @@ struct dma_device {
>> > static inline int dmaengine_slave_config(struct dma_chan *chan,
>> > struct dma_slave_config *config)
>> > {
>> > + if (config->src_maxburst && config->device->src_bursts &&
>> > + !(BIT(config->src_maxburst) & config->device->src_bursts))
>>
>> The maxburst may be as big as 4Kibytes, then, I am not sure that this
>> code will work!
>>
>> > + return -EINVAL;
>> > +
>> > + if (config->dst_maxburst && config->device->dst_bursts &&
>> > + !(BIT(config->dst_maxburst) & config->device->dst_bursts))
>> > + return -EINVAL;
>> > +
>> > if (chan->device->device_config)
>> > return chan->device->device_config(chan, config);
>> > -------8<------------
>>
>> Yes, I know that the burst size is always a power of 2.
>> The best way to check it would be to change the {src,dts}_maxburst to a
>> bitmap of the possible bursts as 0x0d for 1,4 and 8 bytes. But this
>> asks for a lot of changes...
>
> To be honest, I'm not really a big fan of those tree wide changes
> without any way to maintain compatibility. It ends up in a single,
> huge patch if we want to maintain bisectability that just isn't
> reviewable.

Looking at the dmaengine API, I believe we got it wrong.

max_burst in dma_slave_config denotes the largest amount of data
a single transfer should be, as described in dmaengine.h:

* @src_maxburst: the maximum number of words (note: words, as in
* units of the src_addr_width member, not bytes) that can be sent
* in one burst to the device. Typically something like half the
* FIFO depth on I/O peripherals so you don't overflow it. This
* may or may not be applicable on memory sources.
* @dst_maxburst: same as src_maxburst but for destination target
* mutatis mutandis.

The DMA engine driver should be free to select whatever burst size
that doesn't exceed this. So for max_burst = 4, the driver can select
burst = 4 for controllers that do support it, or burst = 1 for those
that don't, and do more bursts.

This also means we can increase max_burst for the audio codec, as
the FIFO is 64 samples deep for stereo, or 128 samples for mono.


If we agree on the above I can send some patches for this.


Regards
ChenYu