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SubjectRe: [PATCH 1/2] dma: at_hdmac: Fix calculation of the residual bytes
Hello Torsten,

On Sun, Feb 08, 2015 at 10:29:03AM +0100, Torsten Fleischer wrote:
> From: Torsten Fleischer <torfl6749@gmail.com>
>
> This patch fixes the following issues regarding to the calculation of the
> residue:
>
> 1. The residue is always calculated for the current transfer even if the
> cookie is associated to a pending transfer.
>
> 2. For scatter/gather DMA the calculation of the residue for the current
> transfer doesn't include the bytes of the child descriptors that are already
> transferred.
> It only calculates the difference between the transfer's total length minus
> the number of bytes that are already transferred for the current child
> descriptor.
> For example: There is a scatter/gather DMA transfer with a total length of
> 1 MByte. Getting the residue several times while the transfer is running shows
> something like that:
>
> 1: residue = 975584
> 2: residue = 1002766
> 3: residue = 992627
> 4: residue = 983767
> 5: residue = 985694
> 6: residue = 1008094
> 7: residue = 1009741
> 8: residue = 1011195
>
> 3. The driver stores the residue but never resets it when starting a new
> transfer.
> For example: If there are two subsequent DMA transfers. The first one with
> a total length of 1 MByte and the second one with a total length of 1 kByte.
> Getting the residue for both transfers shows something like that:
>
> transfer 1: residue = 975584
> transfer 2: residue = 1048380
>

You're right about these points. Good job. I think it should be sent to
stable if it can be applied properly.

For multilines comments, please follow the coding rule
/*
* my
* comments
*/

> Signed-off-by: Torsten Fleischer <torfl6749@gmail.com>

Another comments below. Otherwise

Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>

> ---
> drivers/dma/at_hdmac.c | 151 ++++++++++++++++++++++----------------------
> drivers/dma/at_hdmac_regs.h | 11 ++--
> 2 files changed, 79 insertions(+), 83 deletions(-)
>
> diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c
> index ca9dd26..0fb98a3 100644
> --- a/drivers/dma/at_hdmac.c
> +++ b/drivers/dma/at_hdmac.c
> @@ -233,93 +233,92 @@ static void atc_dostart(struct at_dma_chan *atchan, struct at_desc *first)
> }

[...]

> -/*
> - * atc_get_bytes_left -
> - * Get the number of bytes residue in dma buffer,
> - * @chan: the channel we want to start
> +/**
> + * atc_get_bytes_left - get the number of bytes residue for a cookie
> + * @chan: DMA channel
> + * @cookie: transaction identifier to check status of
> */
> -static int atc_get_bytes_left(struct dma_chan *chan)
> +static int atc_get_bytes_left(struct dma_chan *chan, dma_cookie_t cookie)
> {
> struct at_dma_chan *atchan = to_at_dma_chan(chan);
> - struct at_dma *atdma = to_at_dma(chan->device);
> - int chan_id = atchan->chan_common.chan_id;
> struct at_desc *desc_first = atc_first_active(atchan);
> - struct at_desc *desc_cur;
> + struct at_desc *desc;
> int ret = 0, count = 0;
> + u32 ctrla, dscr;
>
> - /*
> - * Initialize necessary values in the first time.
> - * remain_desc record remain desc length.
> - */
> - if (atchan->remain_desc == 0)
> - /* First descriptor embedds the transaction length */
> - atchan->remain_desc = desc_first->len;
> + /* If the cookie doesn't match to the currently running transfer then
> + * we can return the total length of the associated DMA transfer,
> + * because it is still queued. */
> + desc = atc_get_desc_by_cookie(atchan, cookie);
> + if (desc == NULL)
> + return -EINVAL;
> + else if (desc != desc_first)
> + return desc->total_len;
>
> - /*
> - * This happens when current descriptor transfer complete.
> - * The residual buffer size should reduce current descriptor length.
> - */
> - if (unlikely(test_bit(ATC_IS_BTC, &atchan->status))) {
> - clear_bit(ATC_IS_BTC, &atchan->status);
> - desc_cur = atc_get_current_descriptors(atchan,
> - channel_readl(atchan, DSCR));
> - if (!desc_cur) {
> - ret = -EINVAL;
> - goto out;
> - }
> + /* cookie matches to the currently running transfer */
> + ret = desc_first->total_len;
> +
> + if (desc_first->lli.dscr) {
> + /* hardware linked list transfer */
> +
> + /* Calculate the residue by removing the length of the child
> + * descriptors already transferred from the total length.
> + * To get the current child descriptor we can use the value of
> + * the channel's DSCR register and compare it against the value
> + * of the hardware linked list structure of each child
> + * descriptor. */
> +
> + dscr = channel_readl(atchan, DSCR);
> +
> + /* the first descriptor is currently in work */
> + if (desc_first->lli.dscr == dscr)
> + return ret;
>

Why returning total_len in this case? I think you can return a more accurate
value as you do for the last descriptor.

> - count = (desc_cur->lli.ctrla & ATC_BTSIZE_MAX)
> - << desc_first->tx_width;
> - if (atchan->remain_desc < count) {
> - ret = -EINVAL;
> - goto out;
> + list_for_each_entry(desc, &desc_first->tx_list, desc_node) {
> + if (desc->lli.dscr == dscr)
> + break;
> +
> + ret -= desc->len;
> }
>
> - atchan->remain_desc -= count;
> - ret = atchan->remain_desc;
> + /* For the last descriptor in the chain we can calculate
> + * the remaining bytes using the channel's register. */
> + if (!desc->lli.dscr) {
> + ctrla = channel_readl(atchan, CTRLA);
> + count = (desc->lli.ctrla & ATC_BTSIZE_MAX) -
> + (ctrla & ATC_BTSIZE_MAX);
> +
> + ret = count << ATC_REG_TO_SRC_WIDTH(ctrla);
> + }
> } else {
> - /*
> - * Get residual bytes when current
> - * descriptor transfer in progress.
> - */
> - count = (channel_readl(atchan, CTRLA) & ATC_BTSIZE_MAX)
> - << (desc_first->tx_width);
> - ret = atchan->remain_desc - count;
> + /* single transfer */
> + ctrla = channel_readl(atchan, CTRLA);
> + count = (ctrla & ATC_BTSIZE_MAX) << ATC_REG_TO_SRC_WIDTH(ctrla);
> + ret -= count;
> }
> - /*
> - * Check fifo empty.
> - */
> - if (!(dma_readl(atdma, CHSR) & AT_DMA_EMPT(chan_id)))
> - atc_issue_pending(chan);
>
> -out:
> return ret;
> }

[...]


Regards

Ludovic


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