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Date: Wed, 20 Jun 2018 15:15:11 +0200
From: Andrea Merello <andrea.merello@...il.com>
To: Radhey Shyam Pandey <radheys@...inx.com>
Cc: "vkoul@...nel.org" <vkoul@...nel.org>,
"dan.j.williams@...el.com" <dan.j.williams@...el.com>,
Michal Simek <michals@...inx.com>,
Appana Durga Kedareswara Rao <appanad@...inx.com>,
"dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] dmaengine: xilinx_dma: fix splitting transfer causes misalignments
On Wed, Jun 20, 2018 at 1:37 PM, Radhey Shyam Pandey <radheys@...inx.com> wrote:
>> -----Original Message-----
>> From: dmaengine-owner@...r.kernel.org [mailto:dmaengine-
>> owner@...r.kernel.org] On Behalf Of Andrea Merello
>> Sent: Wednesday, June 20, 2018 2:07 PM
>> To: vkoul@...nel.org; dan.j.williams@...el.com; Michal Simek
>> <michals@...inx.com>; Appana Durga Kedareswara Rao
>> <appanad@...inx.com>; dmaengine@...r.kernel.org
>> Cc: linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org;
>> Andrea Merello <andrea.merello@...il.com>
>> Subject: [PATCH 1/6] dmaengine: xilinx_dma: fix splitting transfer causes
>> misalignments
>
> We should rephrase commit message to something like "In axidma
> slave_sg and dma_cylic mode align split descriptors"
OK
>>
>> Whenever a single or cyclic transaction is prepared, the driver
>> could eventually split it over several SG descriptors in order
>> to deal with the HW maximum transfer length.
>>
>> This could end up in DMA operations starting from a misaligned
>> address. This seems fatal for the HW.
> This seems fatal for the HW if DRE is not enabled.
OK
>>
>> This patch eventually adjusts the transfer size in order to make sure
>> all operations start from an aligned address.
>>
>> Signed-off-by: Andrea Merello <andrea.merello@...il.com>
>> ---
>> drivers/dma/xilinx/xilinx_dma.c | 27 ++++++++++++++++++++-------
>> 1 file changed, 20 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
>> index 27b523530c4a..a516e7ffef21 100644
>> --- a/drivers/dma/xilinx/xilinx_dma.c
>> +++ b/drivers/dma/xilinx/xilinx_dma.c
>> @@ -376,6 +376,7 @@ struct xilinx_dma_chan {
>> void (*start_transfer)(struct xilinx_dma_chan *chan);
>> int (*stop_transfer)(struct xilinx_dma_chan *chan);
>> u16 tdest;
>> + u32 copy_mask;
> We can reuse copy_align itself. See below.
OK
>> };
>>
>> /**
>> @@ -1789,10 +1790,14 @@ static struct dma_async_tx_descriptor
>> *xilinx_dma_prep_slave_sg(
>>
>> /*
>> * Calculate the maximum number of bytes to transfer,
>> - * making sure it is less than the hw limit
>> + * making sure it is less than the hw limit and that
>> + * the next chuck start address is aligned
>
> /s/chuck/chunk
OK
>> */
>> - copy = min_t(size_t, sg_dma_len(sg) - sg_used,
>> - XILINX_DMA_MAX_TRANS_LEN);
>> + copy = sg_dma_len(sg) - sg_used;
>> + if (copy > XILINX_DMA_MAX_TRANS_LEN)
>> + copy = XILINX_DMA_MAX_TRANS_LEN &
>> + chan->copy_mask;
>> +
>
>
> In below implementation, we can reuse copy_align.
> Same for dma_cyclic.
>
> if ((copy + sg_used < sg_dma_len(sg)) &&
> chan->xdev->common.copy_align) {
> /* If this is not the last descriptor, make sure
> * the next one will be properly aligned
> */
> copy = rounddown(copy,
> (1 << chan->xdev->common.copy_align));
> }
OK for the general idea. But to me it seems a bit more complicated than needed:
What's the point in setting 'copy' with min_t, performing also the
subtraction sg_dma_len(sg) - sg_used, and then add sg_used again? What
about something like:
- copy = min_t(size_t, sg_dma_len(sg) - sg_used,
- XILINX_DMA_MAX_TRANS_LEN);
+ copy = sg_dma_len(sg) - sg_used;
+ if (copy > XILINX_DMA_MAX_TRANS_LEN &&
+ chan->xdev->common.copy_align)
+ copy = rounddown(XILINX_DMA_MAX_TRANS_LEN,
+ (1 << chan->xdev->common.copy_align));
+
>> hw = &segment->hw;
>>
>> /* Fill in the descriptor */
>> @@ -1894,10 +1899,14 @@ static struct dma_async_tx_descriptor
>> *xilinx_dma_prep_dma_cyclic(
>>
>> /*
>> * Calculate the maximum number of bytes to transfer,
>> - * making sure it is less than the hw limit
>> + * making sure it is less than the hw limit and that
>> + * the next chuck start address is aligned
>> */
>> - copy = min_t(size_t, period_len - sg_used,
>> - XILINX_DMA_MAX_TRANS_LEN);
>> + copy = period_len - sg_used;
>> + if (copy > XILINX_DMA_MAX_TRANS_LEN)
>> + copy = XILINX_DMA_MAX_TRANS_LEN &
>> + chan->copy_mask;
>> +
>> hw = &segment->hw;
>> xilinx_axidma_buf(chan, hw, buf_addr, sg_used,
>> period_len * i);
>> @@ -2402,8 +2411,12 @@ static int xilinx_dma_chan_probe(struct
>> xilinx_dma_device *xdev,
>> if (width > 8)
>> has_dre = false;
>>
>> - if (!has_dre)
>> + if (has_dre) {
>> + chan->copy_mask = ~0;
>> + } else {
>> xdev->common.copy_align = fls(width - 1);
>> + chan->copy_mask = ~(width - 1);
>> + }
>
> As mentioned above we don't need this additional field.
OK
>>
>> if (of_device_is_compatible(node, "xlnx,axi-vdma-mm2s-channel") ||
>> of_device_is_compatible(node, "xlnx,axi-dma-mm2s-channel") ||
>> --
>> 2.17.1
>>
>> --
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