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

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Message-ID: <20140919102212.GA31784@xps8300>
Date:	Fri, 19 Sep 2014 13:22:12 +0300
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
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 Wed, Sep 17, 2014 at 06:34:45PM +0200, Sebastian Andrzej Siewior wrote:
> 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

Couldn't you just replace the handle_irq with a custom irq routine in
the omap driver like you did with set_termios? Where you would do
those tricks and/or call serial8250_handle_irq()?

The 8250_core changes in that patch #10 only modify
serial8250_handle_irg right?


Cheers,

-- 
heikki
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