linux-kernel - Re: [PATCH v2 02/15] spi: dw: update NDF while using enhanced spi mode

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Date:   Mon, 9 Jan 2023 19:52:44 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Sudip Mukherjee <sudip.mukherjee@...ive.com>
Cc:     Mark Brown <broonie@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        jude.onyenegecha@...ive.com, ben.dooks@...ive.com,
        jeegar.lakhani@...ive.com, linux-spi@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 02/15] spi: dw: update NDF while using enhanced spi
 mode

On Mon, Dec 12, 2022 at 06:07:19PM +0000, Sudip Mukherjee wrote:
> If the transfer of Transmit only mode is using dual/quad/octal SPI then
> NDF needs to be updated with the number of data frames.
> If the Transmit FIFO goes empty in-between, DWC_ssi masks the serial
> clock and wait for rest of the data until the programmed amount of
> frames are transferred successfully.
> 
> Signed-off-by: Sudip Mukherjee <sudip.mukherjee@...ive.com>
> ---
>  drivers/spi/spi-dw-core.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/spi/spi-dw-core.c b/drivers/spi/spi-dw-core.c
> index 77c23772bb3d9..8c47a4d14b666 100644
> --- a/drivers/spi/spi-dw-core.c
> +++ b/drivers/spi/spi-dw-core.c
> @@ -346,7 +346,9 @@ void dw_spi_update_config(struct dw_spi *dws, struct spi_device *spi,
>  	dw_writel(dws, DW_SPI_CTRLR0, cr0);
>  
>  	if (cfg->tmode == DW_SPI_CTRLR0_TMOD_EPROMREAD ||

> -	    cfg->tmode == DW_SPI_CTRLR0_TMOD_RO)
> +	    cfg->tmode == DW_SPI_CTRLR0_TMOD_RO ||
> +	    (cfg->tmode == DW_SPI_CTRLR0_TMOD_TO &&
> +	     cfg->spi_frf != DW_SPI_CTRLR0_SPI_FRF_STD_SPI))

First CTRLR1.NDF is meaningful for the Tx-only mode if non-zero eSPI
mode is enabled and the clock-stretching feature is activated. Second
the conditional statement already looks too bulky. Adding new parts
will make it even harder to read. What about converting it to
something like:

< if (cfg->ndf)
< 	dw_writel(dws, DW_SPI_CTRLR1, cfg->ndf - 1);

What do you think?

-Serge(y)

>  		dw_writel(dws, DW_SPI_CTRLR1, cfg->ndf ? cfg->ndf - 1 : 0);
>  
>  	/* Note DW APB SSI clock divider doesn't support odd numbers */
> -- 
> 2.30.2
>