linux-kernel - Re: [PATCH v5 6/7] dmaengine: idxd: Support device_tx

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Date:   Thu, 1 Sep 2022 10:24:13 -0700
From:   Dave Jiang <dave.jiang@...el.com>
To:     Ben Walker <benjamin.walker@...el.com>, vkoul@...nel.org
Cc:     dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
        Fenghua Yu <fenghua.yu@...el.com>
Subject: Re: [PATCH v5 6/7] dmaengine: idxd: Support device_tx_status


On 8/29/2022 1:35 PM, Ben Walker wrote:
> This can now be supported even for devices that complete operations out
> of order. Add support for directly polling transactions.
>
> Cc: Dave Jiang <dave.jiang@...el.com>
> Cc: Fenghua Yu <fenghua.yu@...el.com>
> Signed-off-by: Ben Walker <benjamin.walker@...el.com>
> ---
>   drivers/dma/idxd/device.c |  1 +
>   drivers/dma/idxd/dma.c    | 85 ++++++++++++++++++++++++++++++++++++++-
>   drivers/dma/idxd/idxd.h   |  1 +
>   3 files changed, 85 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma/idxd/device.c b/drivers/dma/idxd/device.c
> index 5a8cc52c1abfd..752544bef4551 100644
> --- a/drivers/dma/idxd/device.c
> +++ b/drivers/dma/idxd/device.c
> @@ -148,6 +148,7 @@ int idxd_wq_alloc_resources(struct idxd_wq *wq)
>   			desc->iax_completion = &wq->iax_compls[i];
>   		desc->compl_dma = wq->compls_addr + idxd->data->compl_size * i;
>   		desc->id = i;
> +		desc->gen = 1;
>   		desc->wq = wq;
>   		desc->cpu = -1;
>   	}
> diff --git a/drivers/dma/idxd/dma.c b/drivers/dma/idxd/dma.c
> index e0874cb4721c8..dda5342d273f4 100644
> --- a/drivers/dma/idxd/dma.c
> +++ b/drivers/dma/idxd/dma.c
> @@ -12,6 +12,23 @@
>   #include "registers.h"
>   #include "idxd.h"
>   
> +
> +#define DMA_COOKIE_BITS (sizeof(dma_cookie_t) * 8)
> +/*
> + * The descriptor id takes the lower 16 bits of the cookie.
> + */
> +#define DESC_ID_BITS 16
> +#define DESC_ID_MASK ((1 << DESC_ID_BITS) - 1)
> +/*
> + * The 'generation' is in the upper half of the cookie. But dma_cookie_t
> + * is signed, so we leave the upper-most bit for the sign. Further, we
> + * need to flag whether a cookie corresponds to an operation that is
> + * being completed via interrupt to avoid polling it, which takes
> + * the second most upper bit. So we subtract two bits from the upper half.
> + */
> +#define DESC_GEN_MAX ((1 << (DMA_COOKIE_BITS - DESC_ID_BITS - 2)) - 1)
> +#define DESC_INTERRUPT_FLAG (1 << (DMA_COOKIE_BITS - 2))
> +
>   static inline struct idxd_wq *to_idxd_wq(struct dma_chan *c)
>   {
>   	struct idxd_dma_chan *idxd_chan;
> @@ -158,13 +175,67 @@ static void idxd_dma_free_chan_resources(struct dma_chan *chan)
>   		idxd_wq_refcount(wq));
>   }
>   
> +

Stray blank line

DJ

>   static enum dma_status idxd_dma_tx_status(struct dma_chan *dma_chan,
>   					  dma_cookie_t cookie,
>   					  struct dma_tx_state *txstate)
>   {
> -	return DMA_OUT_OF_ORDER;
> +	u8 status;
> +	struct idxd_wq *wq;
> +	struct idxd_desc *desc;
> +	u32 idx;
> +
> +	memset(txstate, 0, sizeof(*txstate));
> +
> +	if (dma_submit_error(cookie))
> +		return DMA_ERROR;
> +
> +	wq = to_idxd_wq(dma_chan);
> +
> +	idx = cookie & DESC_ID_MASK;
> +	if (idx >= wq->num_descs)
> +		return DMA_ERROR;
> +
> +	desc = wq->descs[idx];
> +
> +	if (desc->txd.cookie != cookie) {
> +		/*
> +		 * The user asked about an old transaction
> +		 */
> +		return DMA_COMPLETE;
> +	}
> +
> +	/*
> +	 * For descriptors completed via interrupt, we can't go
> +	 * look at the completion status directly because it races
> +	 * with the IRQ handler recyling the descriptor. However,
> +	 * since in this case we can rely on the interrupt handler
> +	 * to invalidate the cookie when the command completes we
> +	 * know that if we get here, the command is still in
> +	 * progress.
> +	 */
> +	if ((cookie & DESC_INTERRUPT_FLAG) != 0)
> +		return DMA_IN_PROGRESS;
> +
> +	status = desc->completion->status & DSA_COMP_STATUS_MASK;
> +
> +	if (status) {
> +		/*
> +		 * Check against the original status as ABORT is software defined
> +		 * and 0xff, which DSA_COMP_STATUS_MASK can mask out.
> +		 */
> +		if (unlikely(desc->completion->status == IDXD_COMP_DESC_ABORT))
> +			idxd_dma_complete_txd(desc, IDXD_COMPLETE_ABORT, true);
> +		else
> +			idxd_dma_complete_txd(desc, IDXD_COMPLETE_NORMAL, true);
> +
> +		return DMA_COMPLETE;
> +	}
> +
> +	return DMA_IN_PROGRESS;
>   }
>   
> +
>   /*
>    * issue_pending() does not need to do anything since tx_submit() does the job
>    * already.
> @@ -181,7 +252,17 @@ static dma_cookie_t idxd_dma_tx_submit(struct dma_async_tx_descriptor *tx)
>   	int rc;
>   	struct idxd_desc *desc = container_of(tx, struct idxd_desc, txd);
>   
> -	cookie = dma_cookie_assign(tx);
> +	cookie = (desc->gen << DESC_ID_BITS) | (desc->id & DESC_ID_MASK);
> +
> +	if ((desc->hw->flags & IDXD_OP_FLAG_RCI) != 0)
> +		cookie |= DESC_INTERRUPT_FLAG;
> +
> +	if (desc->gen == DESC_GEN_MAX)
> +		desc->gen = 1;
> +	else
> +		desc->gen++;
> +
> +	tx->cookie = cookie;
>   
>   	rc = idxd_submit_desc(wq, desc);
>   	if (rc < 0) {
> diff --git a/drivers/dma/idxd/idxd.h b/drivers/dma/idxd/idxd.h
> index bd93ada32c89d..d4f0227895075 100644
> --- a/drivers/dma/idxd/idxd.h
> +++ b/drivers/dma/idxd/idxd.h
> @@ -326,6 +326,7 @@ struct idxd_desc {
>   	struct llist_node llnode;
>   	struct list_head list;
>   	u16 id;
> +	u16 gen;
>   	int cpu;
>   	struct idxd_wq *wq;
>   };