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Subject: Re: [PATCH] Revert "spi: omap2-mcspi: Set FIFO DMA trigger level to
 word length"
To:     linux-spi@vger.kernel.org
Cc:     Mark Brown <broonie@kernel.org>, linux-kernel@vger.kernel.org,
        Vignesh R <vigneshr@ti.com>, linux-omap@vger.kernel.org
References: <20190113204905.29795-1-david@lechnology.com>
From:   David Lechner <david@lechnology.com>
Message-ID: <7a88c1be-3737-caad-7e8f-5651cbe23248@lechnology.com>
Date:   Sun, 13 Jan 2019 14:52:37 -0600
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CC: OMAP list for good measure

On 1/13/19 2:49 PM, David Lechner wrote:
> This reverts commit b682cffa3ac6d9d9e16e9b413c45caee3b391fab.
> 
> That commit breaks displays using tinydrm drivers, such as ili9225.
> 
> It causes corruption in the image that is displayed (it looks like only
> 1/2 of the framebuffer data is sent, the other half of the display
> remains blank.)
> 
> The following error appears multiple times:
> 
>      ili9225 spi1.0: EOW timed out
> 
> Eventually, the system locks up without any additional errors.
> 
> Cc: Vignesh R <vigneshr@ti.com>
> Signed-off-by: David Lechner <david@lechnology.com>
> ---
>   drivers/spi/spi-omap2-mcspi.c | 26 +++++++++++++++++++-------
>   1 file changed, 19 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/spi/spi-omap2-mcspi.c b/drivers/spi/spi-omap2-mcspi.c
> index 2fd8881fcd65..5a3854ff2e08 100644
> --- a/drivers/spi/spi-omap2-mcspi.c
> +++ b/drivers/spi/spi-omap2-mcspi.c
> @@ -306,7 +306,7 @@ static void omap2_mcspi_set_fifo(const struct spi_device *spi,
>   	struct omap2_mcspi_cs *cs = spi->controller_state;
>   	struct omap2_mcspi *mcspi;
>   	unsigned int wcnt;
> -	int max_fifo_depth, bytes_per_word;
> +	int max_fifo_depth, fifo_depth, bytes_per_word;
>   	u32 chconf, xferlevel;
>   
>   	mcspi = spi_master_get_devdata(master);
> @@ -322,6 +322,10 @@ static void omap2_mcspi_set_fifo(const struct spi_device *spi,
>   		else
>   			max_fifo_depth = OMAP2_MCSPI_MAX_FIFODEPTH;
>   
> +		fifo_depth = gcd(t->len, max_fifo_depth);
> +		if (fifo_depth < 2 || fifo_depth % bytes_per_word != 0)
> +			goto disable_fifo;
> +
>   		wcnt = t->len / bytes_per_word;
>   		if (wcnt > OMAP2_MCSPI_MAX_FIFOWCNT)
>   			goto disable_fifo;
> @@ -329,17 +333,16 @@ static void omap2_mcspi_set_fifo(const struct spi_device *spi,
>   		xferlevel = wcnt << 16;
>   		if (t->rx_buf != NULL) {
>   			chconf |= OMAP2_MCSPI_CHCONF_FFER;
> -			xferlevel |= (bytes_per_word - 1) << 8;
> +			xferlevel |= (fifo_depth - 1) << 8;
>   		}
> -
>   		if (t->tx_buf != NULL) {
>   			chconf |= OMAP2_MCSPI_CHCONF_FFET;
> -			xferlevel |= bytes_per_word - 1;
> +			xferlevel |= fifo_depth - 1;
>   		}
>   
>   		mcspi_write_reg(master, OMAP2_MCSPI_XFERLEVEL, xferlevel);
>   		mcspi_write_chconf0(spi, chconf);
> -		mcspi->fifo_depth = max_fifo_depth;
> +		mcspi->fifo_depth = fifo_depth;
>   
>   		return;
>   	}
> @@ -598,6 +601,7 @@ omap2_mcspi_txrx_dma(struct spi_device *spi, struct spi_transfer *xfer)
>   	struct dma_slave_config	cfg;
>   	enum dma_slave_buswidth width;
>   	unsigned es;
> +	u32			burst;
>   	void __iomem		*chstat_reg;
>   	void __iomem            *irqstat_reg;
>   	int			wait_res;
> @@ -617,14 +621,22 @@ omap2_mcspi_txrx_dma(struct spi_device *spi, struct spi_transfer *xfer)
>   	}
>   
>   	count = xfer->len;
> +	burst = 1;
> +
> +	if (mcspi->fifo_depth > 0) {
> +		if (count > mcspi->fifo_depth)
> +			burst = mcspi->fifo_depth / es;
> +		else
> +			burst = count / es;
> +	}
>   
>   	memset(&cfg, 0, sizeof(cfg));
>   	cfg.src_addr = cs->phys + OMAP2_MCSPI_RX0;
>   	cfg.dst_addr = cs->phys + OMAP2_MCSPI_TX0;
>   	cfg.src_addr_width = width;
>   	cfg.dst_addr_width = width;
> -	cfg.src_maxburst = es;
> -	cfg.dst_maxburst = es;
> +	cfg.src_maxburst = burst;
> +	cfg.dst_maxburst = burst;
>   
>   	rx = xfer->rx_buf;
>   	tx = xfer->tx_buf;
>