Messages in this thread | | | Date | Fri, 13 May 2016 14:48:27 +0530 | From | charanya@codeauro ... | Subject | Re: [PATCH] tty: serial: msm: Disable restoring Rx interrupts for DMA Mode |
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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@codeaurora.org> >> >> 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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