Re: [RFC RESEND] serial: 8250: fix regression in 8250 uart driver

[Andy Shevchenko <andriy.shevchenko@linux.intel.com>]

On Mon, 2016-06-13 at 21:59 -0500, Dinh Nguyen wrote:
> Apologies, but my original email bounced for Andy and Heikki,
> resending.
> ----

I suppose this one, i.e. commit dd4e91d538b3 ("dmaengine: slave means at
least one of DMA_SLAVE, DMA_CYCLIC"), solves the issue.

> 
> Hi Andy,
> 
> I saw that you have discovered that commit ec5a11a91eec ("serial:
> 8250:
> Validate dmaengine rx chan meets requirements") introduced a
> regression
> in the 8250 uart driver. For SoCFPGA platform, I am seeing this error:
> 
> [    5.541751] ttyS0 - failed to request DMA
> 
> Reverting the commit ec5a11a91eec removes the error.
> 
> I saw that you started the discussion, but I didn't see that a patch
> was
> included[1].
> 
> The following patch seems to fix the error, but I'm not sure if it's
> the
> same fix that you had in mind.
> 
> Thanks,
> Dinh
> 
> [1] http://marc.info/?l=linux-serial&m=146254187602862&w=2
> 
> ---------------8<------------
> diff --git a/drivers/tty/serial/8250/8250_dma.c
> b/drivers/tty/serial/8250/8250_dma.c
> index 7f33d1c..847a203 100644
> --- a/drivers/tty/serial/8250/8250_dma.c
> +++ b/drivers/tty/serial/8250/8250_dma.c
> @@ -176,7 +176,7 @@ int serial8250_request_dma(struct uart_8250_port
> *p)
>         ret = dma_get_slave_caps(dma->rxchan, &caps);
>         if (ret)
>                 goto release_rx;
> -       if (!caps.cmd_pause || !caps.cmd_terminate ||
> +       if ((!caps.cmd_pause || !caps.cmd_terminate) &&
>             caps.residue_granularity ==
> DMA_RESIDUE_GRANULARITY_DESCRIPTOR) {
>                 ret = -EINVAL;
>                 goto release_rx;

-- 

Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Intel Finland Oy