> -----Original Message----- > From: Lucas Stach [mailto:l.stach@xxxxxxxxxxxxxx] > Sent: 2018年7月23日 18:54 > To: Robin Gong <yibin.gong@xxxxxxx>; vkoul@xxxxxxxxxx; > dan.j.williams@xxxxxxxxx; s.hauer@xxxxxxxxxxxxxx; linux@xxxxxxxxxxxxxxx > Cc: dmaengine@xxxxxxxxxxxxxxx; dl-linux-imx <linux-imx@xxxxxxx>; > kernel@xxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; > linux-kernel@xxxxxxxxxxxxxxx > Subject: Re: [PATCH v3 3/3] dmaengine: imx-sdma: allocate max 20 bds for one > transfer > > Am Dienstag, den 24.07.2018, 01:46 +0800 schrieb Robin Gong: > > If multi-bds used in one transfer, all bds should be consisten > > memory.To easily follow it, enlarge the dma pool size into 20 bds, and > > it will report error if the number of bds is over than 20. For > > dmatest, the max count for single transfer is NUM_BD * > SDMA_BD_MAX_CNT > > = 20 * 65535 = ~1.28MB. > > Both the commit message and the comment need a lot more care to actually > tell what this commit is trying to achieve. Currently I don't follow at all. What > does "consisten" mean? Do you mean BDs should be contiguous in memory? Yes, BDs should be contiguous one by one in memory. > > What do you gain by over-allocating each BD by a factor of 20? I guess dma_pool_alloc will return error in such case, and then cause dma setup transfer failure. > > Regards, > Lucas > > > Signed-off-by: Robin Gong <yibin.gong@xxxxxxx> > > --- > > drivers/dma/imx-sdma.c | 17 ++++++++++++++++- > > 1 file changed, 16 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c index > > b4ec2d2..5973489 100644 > > --- a/drivers/dma/imx-sdma.c > > +++ b/drivers/dma/imx-sdma.c > > @@ -298,6 +298,15 @@ struct sdma_context_data { > > > u32 scratch7; > > } __attribute__ ((packed)); > > > > +/* > > + * All bds in one transfer should be consitent on SDMA. To easily > > +follow it,just > > + * set the dma pool size as the enough bds. For example, in dmatest > > +case, the > > + * max 20 bds means the max for single transfer is NUM_BD * > > +SDMA_BD_MAX_CNT = 20 > > + * * 65535 = ~1.28MB. 20 bds supposed to be enough basically.If it's > > +still not > > + * enough in some specific cases, enlarge it here.Warning message > > +would also > > + * appear if the bd numbers is over than 20. > > + */ > > +#define NUM_BD 20 > > > > struct sdma_engine; > > > > @@ -1273,7 +1282,7 @@ static int sdma_alloc_chan_resources(struct > > dma_chan *chan) > > > goto disable_clk_ahb; > > > > > sdmac->bd_pool = dma_pool_create("bd_pool", chan->device->dev, > > > - sizeof(struct sdma_buffer_descriptor), > > > + NUM_BD * sizeof(struct sdma_buffer_descriptor), > > > 32, 0); > > > > > return 0; > > @@ -1314,6 +1323,12 @@ static struct sdma_desc > > *sdma_transfer_init(struct sdma_channel *sdmac, > > { > > > struct sdma_desc *desc; > > > > > + if (bds > NUM_BD) { > > > + dev_err(sdmac->sdma->dev, "%d bds exceed the max %d\n", > > > + bds, NUM_BD); > > > + goto err_out; > > > + } > > + > > > desc = kzalloc((sizeof(*desc)), GFP_NOWAIT); > > > if (!desc) > > > goto err_out; ��.n��������+%������w��{.n��������)�)�� jg��� �����ݢj����G���� ���j:+v���w�m������w�������h�����٥
