linux-kernel - Re: [PATCH RESEND 2/5] spi: imx: Use dynamic bursts only when bits_per

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Date:   Mon, 6 Aug 2018 11:41:11 +0200
From:   Sascha Hauer <s.hauer@...gutronix.de>
To:     Maxime Chevallier <maxime.chevallier@...tlin.com>
Cc:     Mark Brown <broonie@...nel.org>, Shawn Guo <shawnguo@...nel.org>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <fabio.estevam@....com>,
        NXP Linux Team <linux-imx@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-spi@...r.kernel.org,
        linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com,
        alexandre.belloni@...tlin.com
Subject: Re: [PATCH RESEND 2/5] spi: imx: Use dynamic bursts only when
 bits_per_word is 8, 16 or 32

On Tue, Jul 17, 2018 at 04:31:51PM +0200, Maxime Chevallier wrote:
> The dynamic bursts mode allows to group together multiple words into a
> single burst. To do so, it's necessary that words can be packed into the
> 32-bits FIFO entries, so we can't allow using this mode with bit_per_words
> different to 8, 16 or 32.
> 
> This prevents shitfing out extra clock ticks for transfers with

s/shitfing/shifting/

> bit_per_word values not aligned on 8 bits.
> 
> With that , we are sure that only the correct number of bits is
> shifted out at each transfer, so we don't need to mask out the remaining
> parts of the words.
> 
> Signed-off-by: Maxime Chevallier <maxime.chevallier@...tlin.com>

Reviewed-by: Sascha Hauer <s.hauer@...gutronix.de>

Sascha

> ---
>  drivers/spi/spi-imx.c | 23 +++++++++--------------
>  1 file changed, 9 insertions(+), 14 deletions(-)
> 
> diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
> index d75153c995af..ecafbda5ec94 100644
> --- a/drivers/spi/spi-imx.c
> +++ b/drivers/spi/spi-imx.c
> @@ -95,7 +95,6 @@ struct spi_imx_data {
>  	const void *tx_buf;
>  	unsigned int txfifo; /* number of words pushed in tx FIFO */
>  	unsigned int dynamic_burst, read_u32;
> -	unsigned int word_mask;
>  
>  	/* Slave mode */
>  	bool slave_mode;
> @@ -291,7 +290,6 @@ static void spi_imx_buf_rx_swap_u32(struct spi_imx_data *spi_imx)
>  		else if (bytes_per_word == 2)
>  			val = (val << 16) | (val >> 16);
>  #endif
> -		val &= spi_imx->word_mask;
>  		*(u32 *)spi_imx->rx_buf = val;
>  		spi_imx->rx_buf += sizeof(u32);
>  	}
> @@ -322,7 +320,6 @@ static void spi_imx_buf_tx_swap_u32(struct spi_imx_data *spi_imx)
>  
>  	if (spi_imx->tx_buf) {
>  		val = *(u32 *)spi_imx->tx_buf;
> -		val &= spi_imx->word_mask;
>  		spi_imx->tx_buf += sizeof(u32);
>  	}
>  
> @@ -1102,25 +1099,23 @@ static int spi_imx_setupxfer(struct spi_device *spi,
>  	spi_imx->bits_per_word = t->bits_per_word;
>  	spi_imx->speed_hz  = t->speed_hz;
>  
> -	/* Initialize the functions for transfer */
> -	if (spi_imx->devtype_data->dynamic_burst && !spi_imx->slave_mode) {
> -		u32 mask;
> +	/*
> +	 * Initialize the functions for transfer. To transfer non byte-aligned
> +	 * words, we have to use multiple word-size bursts, we can't use
> +	 * dynamic_burst in that case.
> +	 */
> +	if (spi_imx->devtype_data->dynamic_burst && !spi_imx->slave_mode &&
> +	    (spi_imx->bits_per_word == 8 ||
> +	    spi_imx->bits_per_word == 16 ||
> +	    spi_imx->bits_per_word == 32)) {
>  
>  		spi_imx->read_u32  = 1;
>  
> -		mask = (1 << spi_imx->bits_per_word) - 1;
>  		spi_imx->rx = spi_imx_buf_rx_swap;
>  		spi_imx->tx = spi_imx_buf_tx_swap;
>  		spi_imx->dynamic_burst = 1;
>  		spi_imx->remainder = t->len;
>  
> -		if (spi_imx->bits_per_word <= 8)
> -			spi_imx->word_mask = mask << 24 | mask << 16
> -					     | mask << 8 | mask;
> -		else if (spi_imx->bits_per_word <= 16)
> -			spi_imx->word_mask = mask << 16 | mask;
> -		else
> -			spi_imx->word_mask = mask;
>  	} else {
>  		if (spi_imx->bits_per_word <= 8) {
>  			spi_imx->rx = spi_imx_buf_rx_u8;
> -- 
> 2.11.0
> 
> 

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