From mboxrd@z Thu Jan  1 00:00:00 1970
From: heikki.krogerus@linux.intel.com (Heikki Krogerus)
Date: Fri, 19 Sep 2014 13:22:12 +0300
Subject: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround
 for AM33xx
In-Reply-To: <5419B825.5000201@linutronix.de>
References: <1410377411-26656-1-git-send-email-bigeasy@linutronix.de>
 <1410377411-26656-10-git-send-email-bigeasy@linutronix.de>
 <20140911111721.GB17476@xps8300> <54118AAB.2010205@linutronix.de>
 <5419B825.5000201@linutronix.de>
Message-ID: <20140919102212.GA31784@xps8300>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org
Archived-At: <https://lore.kernel.org/linux-arm-kernel/20140919102212.GA31784@xps8300/>
List-Archive: <https://lore.kernel.org/linux-arm-kernel/>
List-Post: <mailto:linux-arm-kernel@lists.infradead.org>

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