On 2016-05-12 10:32, Andy Gross wrote:
On Wed, May 11, 2016 at 06:41:26PM -0700, Stephen Boyd wrote:
On 05/10, Abhishek Sahu wrote:
> From: Charanya <charanya@xxxxxxxxxxxxxx>
Was it intentional to only have one name here?
>
> The Data loss was happening with current QCOM MSM serial driver during
> large file transfer due to simultaneous enabling of both UART and
> DMA interrupt. When UART operates in DMA mode, RXLEV (Rx FIFO over
> watermark) or RXSTALE (stale interrupts) should not be enabled,
> since these conditions will be handled by DMA controller itself.
> If these interrupts are enabled then normal UART ISR will read some
> bytes of data from Rx Buffer and DMA controller will not receive
> these bytes of data, which will cause data loss.
>
> Now this patch removed the code for enabling of RXLEV and RXSTALE
> interrupt in DMA Rx completion routine.
I'm lost, we keep both these irqs masked (well only if uartdm
version is 1.4 or greater) pretty much the entire time we're
using DMA for RX. msm_start_rx_dma() will mask them and then when
the callback completes we'll unmask them (the part that's deleted
in this patch), but then we'll go back and remask them almost
immediately because we call msm_start_rx_dma() from the dma
completion handler.
Can you clearly describe how this is actually fixing any
problems? What's the sequence of events that happens to cause
corruption?
This does raise the question though why we ever mask/unmask these
interrupts if we're always going to keep them masked while doing
DMA RX. Presumably if we can use DMA to RX, we can always use it
and set things up properly at startup time instead of later on.
Thats probably the right thing to do. We shouldn't be
masking/unmasking
the unused IRQs to begin with.
Hi Stephen/Andy,
If both Tx and Rx are used simultaneously, restoring Rx interrupts in
msm_complete_rx_dma could lead to RXSTALE interrupt being triggered,
when
the ISR execution for TXLEV interrupt is completed, since msm_port->imr
is
rewritten to UART_IMR in msm_uart_irq. Hence, we do not have to restore
Rx interrupts since Rx is always in DMA mode once enabled.
Thanks.
Charanya.
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