Re: [PATCH v3 01/16] spi: dw: Add Tx/Rx finish wait methods to the MID DMA

[Feng Tang <feng.tang@xxxxxxxxx>]

Hi Serge,

On Thu, May 21, 2020 at 04:21:51AM +0300, Serge Semin wrote:
> Since DMA transfers are performed asynchronously with actual SPI
> transaction, then even if DMA transfers are finished it doesn't mean
> all data is actually pushed to the SPI bus. Some data might still be
> in the controller FIFO. This is specifically true for Tx-only
> transfers. In this case if the next SPI transfer is recharged while
> a tail of the previous one is still in FIFO, we'll loose that tail
> data. In order to fix this lets add the wait procedure of the Tx/Rx
> SPI transfers completion after the corresponding DMA transactions
> are finished.
> 
> Co-developed-by: Georgy Vlasov <Georgy.Vlasov@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Georgy Vlasov <Georgy.Vlasov@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Serge Semin <Sergey.Semin@xxxxxxxxxxxxxxxxxxxx>
> Fixes: 7063c0d942a1 ("spi/dw_spi: add DMA support")
> Cc: Ramil Zaripov <Ramil.Zaripov@xxxxxxxxxxxxxxxxxxxx>
> Cc: Alexey Malahov <Alexey.Malahov@xxxxxxxxxxxxxxxxxxxx>
> Cc: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
> Cc: Paul Burton <paulburton@xxxxxxxxxx>
> Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> Cc: Rob Herring <robh+dt@xxxxxxxxxx>
> Cc: linux-mips@xxxxxxxxxxxxxxx
> Cc: devicetree@xxxxxxxxxxxxxxx
> 
> ---
> 
> Changelog v2:
> - Use conditional statement instead of the ternary operator in the ref
>   clock getter.
> - Move the patch to the head of the series so one could be picked up to
>   the stable kernels as a fix.
> 
> Changelog v3:
> - Use spi_delay_exec() method to wait for the current operation completion.
> ---
>  drivers/spi/spi-dw-mid.c | 69 ++++++++++++++++++++++++++++++++++++++++
>  drivers/spi/spi-dw.h     | 10 ++++++
>  2 files changed, 79 insertions(+)
> 
> diff --git a/drivers/spi/spi-dw-mid.c b/drivers/spi/spi-dw-mid.c
> index f9757a370699..3526b196a7fc 100644
> --- a/drivers/spi/spi-dw-mid.c
> +++ b/drivers/spi/spi-dw-mid.c
> @@ -17,6 +17,7 @@
>  #include <linux/pci.h>
>  #include <linux/platform_data/dma-dw.h>
>  
> +#define WAIT_RETRIES	5
>  #define RX_BUSY		0
>  #define TX_BUSY		1
>  
> @@ -143,6 +144,47 @@ static enum dma_slave_buswidth convert_dma_width(u32 dma_width) {
>  	return DMA_SLAVE_BUSWIDTH_UNDEFINED;
>  }
>  
> +static void dw_spi_dma_calc_delay(struct dw_spi *dws, u32 nents,
> +				  struct spi_delay *delay)
> +{
> +	unsigned long ns, us;
> +
> +	ns = (NSEC_PER_SEC / spi_get_clk(dws)) * nents * dws->n_bytes *
> +	     BITS_PER_BYTE;
> +
> +	if (ns <= NSEC_PER_USEC) {
> +		delay->unit = SPI_DELAY_UNIT_NSECS;
> +		delay->value = ns;
> +	} else {
> +		us = DIV_ROUND_UP(ns, NSEC_PER_USEC);
> +		delay->unit = SPI_DELAY_UNIT_USECS;
> +		delay->value = clamp_val(us, 0, USHRT_MAX);
> +	}
> +}
> +
> +static inline bool dw_spi_dma_tx_busy(struct dw_spi *dws)
> +{
> +	return !(dw_readl(dws, DW_SPI_SR) & SR_TF_EMPT);
> +}
> +
> +static void dw_spi_dma_wait_tx_done(struct dw_spi *dws)
> +{
> +	int retry = WAIT_RETRIES;
> +	struct spi_delay delay;
> +	u32 nents;
> +
> +	nents = dw_readl(dws, DW_SPI_TXFLR);
> +	dw_spi_dma_calc_delay(dws, nents, &delay);
> +
> +	while (dw_spi_dma_tx_busy(dws) && retry--)
> +		spi_delay_exec(&delay, NULL);
> +
> +	if (retry < 0) {
> +		dev_err(&dws->master->dev, "Tx hanged up\n");
> +		dws->master->cur_msg->status = -EIO;
> +	}
> +}
> +
>  /*
>   * dws->dma_chan_busy is set before the dma transfer starts, callback for tx
>   * channel will clear a corresponding bit.
> @@ -151,6 +193,8 @@ static void dw_spi_dma_tx_done(void *arg)
>  {
>  	struct dw_spi *dws = arg;
>  
> +	dw_spi_dma_wait_tx_done(dws);
> +
>  	clear_bit(TX_BUSY, &dws->dma_chan_busy);
>  	if (test_bit(RX_BUSY, &dws->dma_chan_busy))
>  		return;
> @@ -192,6 +236,29 @@ static struct dma_async_tx_descriptor *dw_spi_dma_prepare_tx(struct dw_spi *dws,
>  	return txdesc;
>  }
>  
> +static inline bool dw_spi_dma_rx_busy(struct dw_spi *dws)
> +{
> +	return !!(dw_readl(dws, DW_SPI_SR) & SR_RF_NOT_EMPT);
> +}
> +
> +static void dw_spi_dma_wait_rx_done(struct dw_spi *dws)
> +{
> +	int retry = WAIT_RETRIES;
> +	struct spi_delay delay;
> +	u32 nents;
> +
> +	nents = dw_readl(dws, DW_SPI_RXFLR);
> +	dw_spi_dma_calc_delay(dws, nents, &delay);
> +
> +	while (dw_spi_dma_rx_busy(dws) && retry--)
> +		spi_delay_exec(&delay, NULL);
> +
> +	if (retry < 0) {
> +		dev_err(&dws->master->dev, "Rx hanged up\n");
> +		dws->master->cur_msg->status = -EIO;
> +	}
> +}
> +
>  /*
>   * dws->dma_chan_busy is set before the dma transfer starts, callback for rx
>   * channel will clear a corresponding bit.
> @@ -200,6 +267,8 @@ static void dw_spi_dma_rx_done(void *arg)
>  {
>  	struct dw_spi *dws = arg;
>  
> +	dw_spi_dma_wait_rx_done(dws);

I can understand the problem about TX, but I don't see how RX
will get hurt, can you elaborate more? thanks

- Feng


> +
>  	clear_bit(RX_BUSY, &dws->dma_chan_busy);
>  	if (test_bit(TX_BUSY, &dws->dma_chan_busy))
>  		return;
> diff --git a/drivers/spi/spi-dw.h b/drivers/spi/spi-dw.h
> index e92d43b9a9e6..81364f501b7e 100644
> --- a/drivers/spi/spi-dw.h
> +++ b/drivers/spi/spi-dw.h
> @@ -210,6 +210,16 @@ static inline void spi_set_clk(struct dw_spi *dws, u16 div)
>  	dw_writel(dws, DW_SPI_BAUDR, div);
>  }
>  
> +static inline u32 spi_get_clk(struct dw_spi *dws)
> +{
> +	u32 div = dw_readl(dws, DW_SPI_BAUDR);
> +
> +	if (!div)
> +		return 0;
> +
> +	return dws->max_freq / div;
> +}
> +
>  /* Disable IRQ bits */
>  static inline void spi_mask_intr(struct dw_spi *dws, u32 mask)
>  {
> -- 
> 2.25.1