linux-kernel - Re: [PATCH] spi: cadence: Add usleep_range() for cdns_spi_fill_tx

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Date:   Fri, 13 Apr 2018 19:03:05 +0100
From:   Mark Brown <broonie@...nel.org>
To:     sxauwsk <sxauwsk@....com>
Cc:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
        guojian <guojian@...oinstrument.net>,
        wangshikai <wangshikai@...o-instrument.cn>
Subject: Re: [PATCH] spi: cadence: Add usleep_range() for
 cdns_spi_fill_tx_fifo()

On Mon, Apr 09, 2018 at 07:16:50PM +0800, sxauwsk wrote:
> In case of xspi work in busy condition, may send bytes failed.
> Add one bytes delay

>  	while ((trans_cnt < CDNS_SPI_FIFO_DEPTH) &&
>  	       (xspi->tx_bytes > 0)) {
> +
> +		/* When xspi in busy condition, bytes may send failed,
> +		 * caused communication failure so add one byte delay
> +		 */
> +		usleep_range(10, 20);
> +
>  		if (xspi->txbuf)
>  			cdns_spi_write(xspi, CDNS_SPI_TXD, *xspi->txbuf++);

This looks like it adds a byte of delay on every read/write - that
seems like a lot of overhead for something that sounds like it's
probably only an issue when the FIFO is full?  Do we need to do this for
every operation, and is it needed for read or is it just write?

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