linux-kernel - Re: [PATCH v3 3/3] spi: s3c64xx: support interrupt based pio mode

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Message-ID: <b93d7b1f-c0b1-7704-2beb-c574f87a06e8@samsung.com>
Date:   Mon, 8 May 2023 10:42:12 +0900
From:   Jaewon Kim <jaewon02.kim@...sung.com>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Andi Shyti <andi@...zian.org>, Mark Brown <broonie@...nel.org>,
        Alim Akhtar <alim.akhtar@...sung.com>
Cc:     linux-spi@...r.kernel.org, linux-samsung-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Chanho Park <chanho61.park@...sung.com>
Subject: Re: [PATCH v3 3/3] spi: s3c64xx: support interrupt based pio mode


On 23. 5. 5. 18:47, Krzysztof Kozlowski wrote:
> On 02/05/2023 08:28, Jaewon Kim wrote:
>> Support interrupt based pio mode to optimize cpu usage.
>> When transmitting data size is larget than 32 bytes, operates with
>> interrupt based pio mode.
>>
>> By using the FIFORDY INT, an interrupt can be triggered when
>> the desired size of data has been received. Using this, we can support
>> interrupt based pio mode.
>>
>> Signed-off-by: Jaewon Kim <jaewon02.kim@...sung.com>
>> ---
>>   drivers/spi/spi-s3c64xx.c | 66 ++++++++++++++++++++++++++++++++++-----
>>   1 file changed, 58 insertions(+), 8 deletions(-)
>>
>> diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
>> index 2a8304678df9..323c6da9730b 100644
>> --- a/drivers/spi/spi-s3c64xx.c
>> +++ b/drivers/spi/spi-s3c64xx.c
>> @@ -58,6 +58,8 @@
>>   #define S3C64XX_SPI_MODE_BUS_TSZ_HALFWORD	(1<<17)
>>   #define S3C64XX_SPI_MODE_BUS_TSZ_WORD		(2<<17)
>>   #define S3C64XX_SPI_MODE_BUS_TSZ_MASK		(3<<17)
>> +#define S3C64XX_SPI_MODE_RX_RDY_LVL		GENMASK(16, 11)
>> +#define S3C64XX_SPI_MODE_RX_RDY_LVL_SHIFT	11
>>   #define S3C64XX_SPI_MODE_SELF_LOOPBACK		(1<<3)
>>   #define S3C64XX_SPI_MODE_RXDMA_ON		(1<<2)
>>   #define S3C64XX_SPI_MODE_TXDMA_ON		(1<<1)
>> @@ -114,6 +116,8 @@
>>   
>>   #define S3C64XX_SPI_TRAILCNT		S3C64XX_SPI_MAX_TRAILCNT
>>   
>> +#define S3C64XX_SPI_POLLING_SIZE	32
>> +
>>   #define msecs_to_loops(t) (loops_per_jiffy / 1000 * HZ * t)
>>   #define is_polling(x)	(x->cntrlr_info->polling)
>>   
>> @@ -552,7 +556,7 @@ static int s3c64xx_wait_for_dma(struct s3c64xx_spi_driver_data *sdd,
>>   }
>>   
>>   static int s3c64xx_wait_for_pio(struct s3c64xx_spi_driver_data *sdd,
>> -				struct spi_transfer *xfer)
>> +				struct spi_transfer *xfer, bool use_irq)
>>   {
>>   	void __iomem *regs = sdd->regs;
>>   	unsigned long val;
>> @@ -573,6 +577,12 @@ static int s3c64xx_wait_for_pio(struct s3c64xx_spi_driver_data *sdd,
>>   	if (RX_FIFO_LVL(status, sdd) < xfer->len)
>>   		usleep_range(time_us / 2, time_us);
>>   
>> +	if (use_irq) {
>> +		val = msecs_to_jiffies(ms);
>> +		if (!wait_for_completion_timeout(&sdd->xfer_completion, val))
>> +			return -EIO;
>> +	}
>> +
>>   	val = msecs_to_loops(ms);
>>   	do {
>>   		status = readl(regs + S3C64XX_SPI_STATUS);
>> @@ -735,10 +745,13 @@ static int s3c64xx_spi_transfer_one(struct spi_master *master,
>>   	void *rx_buf = NULL;
>>   	int target_len = 0, origin_len = 0;
>>   	int use_dma = 0;
>> +	bool use_irq = false;
>>   	int status;
>>   	u32 speed;
>>   	u8 bpw;
>>   	unsigned long flags;
>> +	u32 rdy_lv;
>> +	u32 val;
>>   
>>   	reinit_completion(&sdd->xfer_completion);
>>   
>> @@ -759,17 +772,46 @@ static int s3c64xx_spi_transfer_one(struct spi_master *master,
>>   	    sdd->rx_dma.ch && sdd->tx_dma.ch) {
>>   		use_dma = 1;
>>   
>> -	} else if (xfer->len > fifo_len) {
>> +	} else if (xfer->len >= fifo_len) {
> I don't fully understand this. If len equals to fifo_len, everything
> would fit into FIFO so no need for all this?

If the FIFO is filled with data, TX Overrun & RX Underrun interrupts 
will occur.

In CPU polling, there is no such issue because data is read before an 
interrupt occurs.

And, RDY_LVL has only 6 bits.(max. 63). we cannot set trigger level on 
the FIFO max size.


>>   		tx_buf = xfer->tx_buf;
>>   		rx_buf = xfer->rx_buf;
>>   		origin_len = xfer->len;
>> -
>>   		target_len = xfer->len;
>> -		if (xfer->len > fifo_len)
>> -			xfer->len = fifo_len;
>> +		xfer->len = fifo_len - 1;
>>   	}
>>   
>>   	do {
>> +		/* transfer size is greater than 32, change to IRQ mode */
>> +		if (xfer->len > S3C64XX_SPI_POLLING_SIZE)
>> +			use_irq = true;
>> +
>> +		if (use_irq) {
>> +			reinit_completion(&sdd->xfer_completion);
>> +
>> +			rdy_lv = xfer->len;
> Style is:
>
> /*
>   *
>
>> +			/* Setup RDY_FIFO trigger Level
>> +			 * RDY_LVL =
>> +			 * fifo_lvl up to 64 byte -> N bytes
>> +			 *               128 byte -> RDY_LVL * 2 bytes
>> +			 *               256 byte -> RDY_LVL * 4 bytes
> I don't understand it. Based on this equation for 256 bytes,
> RDY_LVL = RDY_LVL * 4?
> Didn't you mean xfer->len?

In v4, I will change it to the following

/*
  * Trigger Level =
  * (N = value of RDY_LVL field)
  * fifo_lvl up to 64 byte -> N bytes
  *               128 byte -> N * 2 bytes
  *               256 byte -> N * 4 bytes
  */

>
>
> Best regards,
> Krzysztof
>
>

Thanks

Jaewon Kim