Re: [PATCH 03/13] serial: 8250_dma: Support for deferred probing when requesting DMA channels

Peter Ujfalusi
2015-05-27T10:58:25Z

On 05/26/2015 06:08 PM, Tony Lindgren wrote:
> * Peter Ujfalusi <peter.ujfalusi@ti.com> [150526 06:28]:
>> Switch to use ma_request_slave_channel_compat_reason() to request the DMA
>> channels. In case of error, return the error code we received including
>> -EPROBE_DEFER
>>
>> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
>> CC: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>> ---
>> drivers/tty/serial/8250/8250_dma.c | 18 ++++++++----------
>> 1 file changed, 8 insertions(+), 10 deletions(-)
>>
>> diff --git a/drivers/tty/serial/8250/8250_dma.c b/drivers/tty/serial/8250/8250_dma.c
>> index 21d01a491405..a617eca4e97d 100644
>> --- a/drivers/tty/serial/8250/8250_dma.c
>> +++ b/drivers/tty/serial/8250/8250_dma.c
>> @@ -182,21 +182,19 @@ int serial8250_request_dma(struct uart_8250_port *p)
>> dma_cap_set(DMA_SLAVE, mask);
>>
>> /* Get a channel for RX */
>> - dma->rxchan = dma_request_slave_channel_compat(mask,
>> - dma->fn, dma->rx_param,
>> - p->port.dev, "rx");
>> - if (!dma->rxchan)
>> - return -ENODEV;
>> + dma->rxchan = dma_request_slave_channel_compat_reason(mask, dma->fn,
>> + dma->rx_param, p->port.dev, "rx");
>> + if (IS_ERR(dma->rxchan))
>> + return PTR_ERR(dma->rxchan);
>>
>> dmaengine_slave_config(dma->rxchan, &dma->rxconf);
>>
>> /* Get a channel for TX */
>> - dma->txchan = dma_request_slave_channel_compat(mask,
>> - dma->fn, dma->tx_param,
>> - p->port.dev, "tx");
>> - if (!dma->txchan) {
>> + dma->txchan = dma_request_slave_channel_compat_reason(mask, dma->fn,
>> + dma->tx_param, p->port.dev, "tx");
>> + if (IS_ERR(dma->txchan)) {
>> dma_release_channel(dma->rxchan);
>> - return -ENODEV;
>> + return PTR_ERR(dma->txchan);
>> }
>>
>> dmaengine_slave_config(dma->txchan, &dma->txconf);
>
> In general the drivers need to work just fine also without DMA.
>
> Does this handle the case properly where no DMA channel is configured
> for the driver in the dts file?

The 8250 core will fall back to PIO mode if the DMA can not be requested.
At the morning I was looking at the 8250 stack and realized that
serial8250_request_dma() will not be called at driver probe time so this patch
can be ignored and will be dropped from the v2 series.

--
Péter