> +static void sci_request_dma(struct uart_port *port)
> +{
> + struct sci_port *s = to_sci_port(port);
> + struct sh_dmae_slave *param;
> + struct dma_chan *chan;
> + dma_cap_mask_t mask;
> + int nent;
> +
> + dev_dbg(port->dev, "%s: port %d DMA %p\n", __func__,
> + port->line, s->dma_dev);
> +
> + if (!s->dma_dev)
> + return;
> +
> + dma_cap_zero(mask);
> + dma_cap_set(DMA_SLAVE, mask);
> +
> + param = &s->param_tx;
> +
> + /* Slave ID, e.g., SHDMA_SLAVE_SCIF0_TX */
> + param->slave_id = s->slave_tx;
> + param->dma_dev = s->dma_dev;
> +
> + s->cookie_tx = -EINVAL;
> + chan = dma_request_channel(mask, filter, param);
> + dev_dbg(port->dev, "%s: TX: got channel %p\n", __func__, chan);
> + if (chan) {
> + s->chan_tx = chan;
> + sg_init_table(&s->sg_tx, 1);
> + /* UART circular tx buffer is an aligned page. */
> + BUG_ON((int)port->state->xmit.buf & ~PAGE_MASK);
> + sg_set_page(&s->sg_tx, virt_to_page(port->state->xmit.buf),
> + UART_XMIT_SIZE, (int)port->state->xmit.buf & ~PAGE_MASK);
> + nent = dma_map_sg(port->dev, &s->sg_tx, 1, DMA_TO_DEVICE);
> + if (!nent)
> + sci_tx_dma_release(s, false);
> + else
> + dev_dbg(port->dev, "%s: mapped %d@%p to %x\n", __func__,
> + sg_dma_len(&s->sg_tx),
> + port->state->xmit.buf, sg_dma_address(&s->sg_tx));
> +
> + s->sg_len_tx = nent;
> +
> + INIT_WORK(&s->work_tx, work_fn_tx);
> + }
> +
> + param = &s->param_rx;
> +
> + /* Slave ID, e.g., SHDMA_SLAVE_SCIF0_RX */
> + param->slave_id = s->slave_rx;
> + param->dma_dev = s->dma_dev;
> +
> + chan = dma_request_channel(mask, filter, param);
> + dev_dbg(port->dev, "%s: RX: got channel %p\n", __func__, chan);
If dma channel allocation fails how this scenario will be handled,
There is an possibility of dma_request_channel returning -EBUSY,
> + if (chan) {
> + dma_addr_t dma[2];
> + void *buf[2];
> + int i;
> +
> + s->chan_rx = chan;
> +
> + s->buf_len_rx = 2 * max(16, (int)port->fifosize);
> + buf[0] = dma_alloc_coherent(port->dev, s->buf_len_rx * 2,
> + &dma[0], GFP_KERNEL);
> +
> + if (!buf[0]) {
> + dev_warn(port->dev,
> + "failed to allocate dma buffer, using PIO\n");
> + sci_rx_dma_release(s, true);
> + return;
> + }
> +
> + buf[1] = buf[0] + s->buf_len_rx;
> + dma[1] = dma[0] + s->buf_len_rx;
> +
> + for (i = 0; i < 2; i++) {
> + struct scatterlist *sg = &s->sg_rx[i];
> +
> + sg_init_table(sg, 1);
> + sg_set_page(sg, virt_to_page(buf[i]), s->buf_len_rx,
> + (int)buf[i] & ~PAGE_MASK);
> + sg->dma_address = dma[i];
> + sg->dma_length = sg->length;
> + }
> +
> + INIT_WORK(&s->work_rx, work_fn_rx);
> + setup_timer(&s->rx_timer, rx_timer_fn, (unsigned long)s);
> +
> + sci_submit_rx(s);
> + }
> +}
---
Regards,
Govindraj.R
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