linux-kernel - Re: [PATCH] tty: serial: msm: Disable restoring Rx interrupts for DMA Mode

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Date:	Thu, 2 Jun 2016 11:37:18 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	charanya@...eaurora.org
Cc:	Andy Gross <andy.gross@...aro.org>,
	Abhishek Sahu <absahu@...eaurora.org>, agross@...eaurora.org,
	david.brown@...aro.org, gregkh@...uxfoundation.org,
	jslaby@...e.com, linux-soc@...r.kernel.org,
	linux-serial@...r.kernel.org, sricharan@...eaurora.org,
	architt@...eaurora.org, linux-arm-msm@...r.kernel.org,
	ntelkar@...eaurora.org, galak@...eaurora.org,
	linux-kernel@...r.kernel.org, dmaengine@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] tty: serial: msm: Disable restoring Rx interrupts for
 DMA Mode

On 06/02, charanya@...eaurora.org wrote:
> On 2016-05-26 04:16, Stephen Boyd wrote:
> >
> >Ok, but what's the exact sequence of events that happens? I think
> >we unlock the spinlock in the dma completion handler and then the
> >txlev interrupt runs? At that point we may have more data to push
> >out and then rx stale handling runs and corrupts the fifo state?
> >
> >I was hoping for some sort of CPU sequence of events like:
> >
> > CPU0                   CPU1
> > ----                   ----
> >
> > msm_start_rx_dma()
> >                       msm_complete_rx_dma()
> >		        spin_unlock_irqrestore(&port->lock)
> > msm_uart_irq()
> >  msm_handle_rx_dm()
> >   <Read from FIFO and breaks>
> >
> >This patch seems correct, but the commit text isn't fully
> >describing the sequence of events that causes this to happen, so
> >it's taking a while to convince myself that this patch fixes
> >anything.
> 
> 
> The sequence of events is as mentioned. When the TXLEV interrupt
> occurs after the
> spinlock is unlocked, the rx stale handling runs since the
> interrupts are restored
> and hence it corrupts the fifo state.

Ok, care to put such information into the commit text of the
patch and resend then please? It will help us later to recall
what the actual problem was.

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