On 2019-9-23 21:58 Philipp Puschmann <philipp.puschm...@emlix.com> wrote:
> For some years and since many kernel versions there are reports that the RX
> UART SDMA channel stops working at some point. The workaround was to
> disable DMA for RX. This commit fixes the problem itself. Cyclic DMA transfers
> are used by uart and other drivers and these can fail in at least two cases
> where we can run out of descriptors available to the
> engine:
> - Interrupts are disabled for too long and all buffers are filled with
> data, especially in a setup where many small dma transfers are being
> executed only using a tiny part of a single buffer
> - DMA errors (such as generated by baud rate mismatch with imx-uart)
> use up all descriptors before we can react.
>
> In this case, SDMA stops the channel and no further transfers are done until
> the respective channel is disabled and re-enabled. We can check if the
> channel has been stopped and re-enable it then. To distinguish from the the
> case that the channel was stopped by upper-level driver we introduce new
> flag IMX_DMA_ACTIVE.
>
> As sdmac->desc is constant we can move desc out of the loop.
>
> Fixes: 1ec1e82f2510 ("dmaengine: Add Freescale i.MX SDMA support")
> Signed-off-by: Philipp Puschmann <philipp.puschm...@emlix.com>
> Signed-off-by: Jan Luebbe <j...@pengutronix.de>
> Reviewed-by: Lucas Stach <l.st...@pengutronix.de>
> ---
>
> Changelog v5:
> - join with patch version from Jan Luebbe
> - adapt comments and patch descriptions
>
> Changelog v4:
> - fixed the fixes tag
>
> Changelog v3:
> - use correct dma_wmb() instead of dma_wb()
> - add fixes tag
>
> Changelog v2:
> - clarify comment and commit description
>
> drivers/dma/imx-sdma.c | 26 ++++++++++++++++++++++----
> 1 file changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c index
> b42281604e54..0b1d6a62423d 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -383,6 +383,7 @@ struct sdma_channel { };
>
> #define IMX_DMA_SG_LOOP BIT(0)
> +#define IMX_DMA_ACTIVE BIT(1)
>
> #define MAX_DMA_CHANNELS 32
> #define MXC_SDMA_DEFAULT_PRIORITY 1
> @@ -658,6 +659,9 @@ static int sdma_config_ownership(struct
> sdma_channel *sdmac,
>
> static void sdma_enable_channel(struct sdma_engine *sdma, int channel) {
> + struct sdma_channel *sdmac = &sdma->channel[channel];
> +
> + sdmac->flags |= IMX_DMA_ACTIVE;
Add spin_lock_irq protect this flags.
> writel(BIT(channel), sdma->regs + SDMA_H_START); }
>
> @@ -774,16 +778,17 @@ static void sdma_start_desc(struct sdma_channel
> *sdmac)
>
> static void sdma_update_channel_loop(struct sdma_channel *sdmac) {
> + struct sdma_engine *sdma = sdmac->sdma;
> struct sdma_buffer_descriptor *bd;
> + struct sdma_desc *desc = sdmac->desc;
> int error = 0;
> - enum dma_status old_status = sdmac->status;
> + enum dma_status old_status = sdmac->status;
>
> /*
> * loop mode. Iterate over descriptors, re-setup them and
> * call callback function.
> */
> - while (sdmac->desc) {
> - struct sdma_desc *desc = sdmac->desc;
> + while (desc) {
>
> bd = &desc->bd[desc->buf_tail];
>
> @@ -822,6 +827,18 @@ static void sdma_update_channel_loop(struct
> sdma_channel *sdmac)
> if (error)
> sdmac->status = old_status;
> }
> +
> + /* In some situations it may happen that the sdma does not find any
> + * usable descriptor in the ring to put data into. The channel is
> + * stopped then and after having freed some buffers we have to restart
> + * it manually.
> + */
> + if ((sdmac->flags & IMX_DMA_ACTIVE) &&
> + !(readl_relaxed(sdma->regs + SDMA_H_STATSTOP) &
> BIT(sdmac->channel))) {
Seems duplicate checking here, IMX_DMA_ACTIVE is enough.
> + dev_err_ratelimited(sdma->dev, "SDMA channel %d: cyclic transfer
> disabled by HW, reenabling\n",
Would you change the print log to below:
"cyclic bds consumed all,reenableing".?
> + sdmac->channel);
> + writel(BIT(sdmac->channel), sdma->regs + SDMA_H_START);
> + };
> }
>
> static void mxc_sdma_handle_channel_normal(struct sdma_channel *data)
> @@ -1051,7 +1068,8 @@ static int sdma_disable_channel(struct dma_chan
> *chan)
> struct sdma_engine *sdma = sdmac->sdma;
> int channel = sdmac->channel;
>
> - writel_relaxed(BIT(channel), sdma->regs + SDMA_H_STATSTOP);
> + sdmac->flags &= ~IMX_DMA_ACTIVE;
> + writel(BIT(channel), sdma->regs + SDMA_H_STATSTOP);
> sdmac->status = DMA_ERROR;
>
> return 0;
> --
> 2.23.0
