linux-kernel - Re: [PATCH v4 25/27] bus: mhi: ep: Add support for queueing SKBs to the host

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Date:   Mon, 28 Feb 2022 10:51:39 -0600
From:   Alex Elder <elder@...aro.org>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        mhi@...ts.linux.dev
Cc:     quic_hemantk@...cinc.com, quic_bbhatt@...cinc.com,
        quic_jhugo@...cinc.com, vinod.koul@...aro.org,
        bjorn.andersson@...aro.org, dmitry.baryshkov@...aro.org,
        quic_vbadigan@...cinc.com, quic_cang@...cinc.com,
        quic_skananth@...cinc.com, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 25/27] bus: mhi: ep: Add support for queueing SKBs to
 the host

On 2/28/22 6:43 AM, Manivannan Sadhasivam wrote:
> Add support for queueing SKBs to the host over the transfer ring of the
> relevant channel. The mhi_ep_queue_skb() API will be used by the client
> networking drivers to queue the SKBs to the host over MHI bus.
> 
> The host will add ring elements to the transfer ring periodically for
> the device and the device will write SKBs to the ring elements. If a
> single SKB doesn't fit in a ring element (TRE), it will be placed in
> multiple ring elements and the overflow event will be sent for all ring
> elements except the last one. For the last ring element, the EOT event
> will be sent indicating the packet boundary.
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>

Looks good.

Reviewed-by: Alex Elder <elder@...aro.org>

> ---
>   drivers/bus/mhi/ep/main.c | 82 +++++++++++++++++++++++++++++++++++++++
>   include/linux/mhi_ep.h    |  9 +++++
>   2 files changed, 91 insertions(+)
> 
> diff --git a/drivers/bus/mhi/ep/main.c b/drivers/bus/mhi/ep/main.c
> index 63e14d55aa06..25d34cf26fd7 100644
> --- a/drivers/bus/mhi/ep/main.c
> +++ b/drivers/bus/mhi/ep/main.c
> @@ -471,6 +471,88 @@ int mhi_ep_process_ch_ring(struct mhi_ep_ring *ring, struct mhi_ring_element *el
>   	return 0;
>   }
>   
> +/* TODO: Handle partially formed TDs */
> +int mhi_ep_queue_skb(struct mhi_ep_device *mhi_dev, struct sk_buff *skb)
> +{
> +	struct mhi_ep_cntrl *mhi_cntrl = mhi_dev->mhi_cntrl;
> +	struct mhi_ep_chan *mhi_chan = mhi_dev->dl_chan;
> +	struct device *dev = &mhi_chan->mhi_dev->dev;
> +	struct mhi_ring_element *el;
> +	u32 buf_left, read_offset;
> +	struct mhi_ep_ring *ring;
> +	enum mhi_ev_ccs code;
> +	void *read_addr;
> +	u64 write_addr;
> +	size_t tr_len;
> +	u32 tre_len;
> +	int ret;
> +
> +	buf_left = skb->len;
> +	ring = &mhi_cntrl->mhi_chan[mhi_chan->chan].ring;
> +
> +	mutex_lock(&mhi_chan->lock);
> +
> +	do {
> +		/* Don't process the transfer ring if the channel is not in RUNNING state */
> +		if (mhi_chan->state != MHI_CH_STATE_RUNNING) {
> +			dev_err(dev, "Channel not available\n");
> +			ret = -ENODEV;
> +			goto err_exit;
> +		}
> +
> +		if (mhi_ep_queue_is_empty(mhi_dev, DMA_FROM_DEVICE)) {
> +			dev_err(dev, "TRE not available!\n");
> +			ret = -ENOSPC;
> +			goto err_exit;
> +		}
> +
> +		el = &ring->ring_cache[ring->rd_offset];
> +		tre_len = MHI_TRE_DATA_GET_LEN(el);
> +
> +		tr_len = min(buf_left, tre_len);
> +		read_offset = skb->len - buf_left;
> +		read_addr = skb->data + read_offset;
> +		write_addr = MHI_TRE_DATA_GET_PTR(el);
> +
> +		dev_dbg(dev, "Writing %zd bytes to channel (%u)\n", tr_len, ring->ch_id);
> +		ret = mhi_cntrl->write_to_host(mhi_cntrl, read_addr, write_addr, tr_len);
> +		if (ret < 0) {
> +			dev_err(dev, "Error writing to the channel\n");
> +			goto err_exit;
> +		}
> +
> +		buf_left -= tr_len;
> +		/*
> +		 * For all TREs queued by the host for DL channel, only the EOT flag will be set.
> +		 * If the packet doesn't fit into a single TRE, send the OVERFLOW event to
> +		 * the host so that the host can adjust the packet boundary to next TREs. Else send
> +		 * the EOT event to the host indicating the packet boundary.
> +		 */
> +		if (buf_left)
> +			code = MHI_EV_CC_OVERFLOW;
> +		else
> +			code = MHI_EV_CC_EOT;
> +
> +		ret = mhi_ep_send_completion_event(mhi_cntrl, ring, el, tr_len, code);
> +		if (ret) {
> +			dev_err(dev, "Error sending transfer completion event\n");
> +			goto err_exit;
> +		}
> +
> +		mhi_ep_ring_inc_index(ring);
> +	} while (buf_left);
> +
> +	mutex_unlock(&mhi_chan->lock);
> +
> +	return 0;
> +
> +err_exit:
> +	mutex_unlock(&mhi_chan->lock);
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(mhi_ep_queue_skb);
> +
>   static int mhi_ep_cache_host_cfg(struct mhi_ep_cntrl *mhi_cntrl)
>   {
>   	size_t cmd_ctx_host_size, ch_ctx_host_size, ev_ctx_host_size;
> diff --git a/include/linux/mhi_ep.h b/include/linux/mhi_ep.h
> index 74170dad09f6..bd3ffde01f04 100644
> --- a/include/linux/mhi_ep.h
> +++ b/include/linux/mhi_ep.h
> @@ -272,4 +272,13 @@ void mhi_ep_power_down(struct mhi_ep_cntrl *mhi_cntrl);
>    */
>   bool mhi_ep_queue_is_empty(struct mhi_ep_device *mhi_dev, enum dma_data_direction dir);
>   
> +/**
> + * mhi_ep_queue_skb - Send SKBs to host over MHI Endpoint
> + * @mhi_dev: Device associated with the DL channel
> + * @skb: SKBs to be queued
> + *
> + * Return: 0 if the SKBs has been sent successfully, a negative error code otherwise.
> + */
> +int mhi_ep_queue_skb(struct mhi_ep_device *mhi_dev, struct sk_buff *skb);
> +
>   #endif