linux-kernel - Re: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx

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Date:	Wed, 17 Sep 2014 18:34:45 +0200
From:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
CC:	linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	tony@...mide.com, balbi@...com, gregkh@...uxfoundation.org,
	Alan Cox <alan@...ux.intel.com>
Subject: Re: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround
 for AM33xx

On 09/11/2014 01:42 PM, Sebastian Andrzej Siewior wrote:
>> We should add hooks like tx_dma and rx_dma to struct uart_8250_dma so
>> that the probe drivers can replace serial8250_tx_dma and
>> seria8250_rx_dma, like I think Alan already suggested.
> 
> Okay. Wasn't aware that Alan already suggested that.
> I also need a watchdog timer for TX since it seems that on omap3 the
> DMA engine suddenly forgets to continue with DMA…
> 
> If this is really what we want, I would need to refactor a few things…
> 
>> Let's keep serial8250_tx_dma/rx_dma as the default, and not add any
>> quirks to them. Only if there is a very common case should it be
>> handled in those. The case of RX req needing to be sent before data in
>> FIFO maybe one of those, but I'm no sure.
> 
> keep in mind that both (RX & TX bugs/hacks) need also a bit of handling
> in the 8250-core so it works together (like the tx_err member so we
> fall back to manual xmit)

Done. I've kept the RX workarounds in the 8250_dma and moved the TX
part into the omap driver.
I needed to add the 8250_core pieces of patch #10 [0]. Now If you say,
couldn't this done in an other way then I could move the RX workarounds
pieces to the omap driver as well as the interrupt routine. Any
preferences?

[0] [PATCH 10/16] tty: serial: 8250_dma: optimize the xmit path due to
    UART_BUG_DMA_TX

Sebastian

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