[U-Boot] [PATCH v4 01/16] spi: Add zynq qspi controller driver

[Hannes Schmelzer]

Hi there,

i am currently debugging on my zynq zc702 board and therefore i have to 
study the qspi-driver :-)

i've some questions about the implementation details.

On 01.09.2015 08:11, Jagan Teki wrote:
> Added zynq qspi controller driver for Xilinx Zynq APSOC,
> this driver is driver-model driven with devicetree support.
(....)
> +static void zynq_qspi_fill_tx_fifo(struct zynq_qspi_priv *priv, u32 size)
> +{
> +	u32 data = 0;
> +	u32 fifocount = 0;
> +	unsigned len, offset;
> +	struct zynq_qspi_regs *regs = priv->regs;
> +	static const unsigned offsets[4] = {
> +		ZYNQ_QSPI_TXD_00_00_OFFSET, ZYNQ_QSPI_TXD_00_01_OFFSET,
> +		ZYNQ_QSPI_TXD_00_10_OFFSET, ZYNQ_QSPI_TXD_00_11_OFFSET };
> +
> +	while ((fifocount < size) &&
> +			(priv->bytes_to_transfer > 0)) {
> +		if (priv->bytes_to_transfer >= 4) {
> +			if (priv->tx_buf) {
> +				memcpy(&data, priv->tx_buf, 4);
> +				priv->tx_buf += 4;
> +			} else {
> +				data = 0;
> +			}
> +			writel(data, &regs->txd0r);
> +			priv->bytes_to_transfer -= 4;
> +			fifocount++;
> +		} else {
> +			/* Write TXD1, TXD2, TXD3 only if TxFIFO is empty. */
> +			if (!(readl(&regs->isr)
> +					& ZYNQ_QSPI_IXR_TXOW_MASK) &&
> +					!priv->rx_buf)
> +				return;
> +			len = priv->bytes_to_transfer;
> +			zynq_qspi_write_data(priv, &data, len);
> +			offset = (priv->rx_buf) ? offsets[0] : offsets[len];
> +			writel(data, &regs->cr + (offset / 4));
I do not understand "offset / 4", if priv->rx_buf == NULL we have an 
offset of 0x1C / 4 --> 7, this end in a write to an unaligned register 
address.
What is the purpose of this ?
> +		}
> +	}
> +}
> +
best regards,
Hannes