IPlib: spi: possible invalid SPI FIFO read

[foxhoundsk]

In the following SPI RX FIFO consumption while-loop:

embeddedsw/XilinxProcessorIPLib/drivers/spi/src/xspi.c

Lines 746 to 783 in 1bb19ac

	while ((StatusReg & XSP_SR_RX_EMPTY_MASK) == 0) {
	Data = XSpi_ReadReg(InstancePtr->BaseAddr,
	XSP_DRR_OFFSET);
	if (DataWidth == XSP_DATAWIDTH_BYTE) {
	/*
	* Data Transfer Width is Byte (8 bit).
	*/
	if(InstancePtr->RecvBufferPtr != NULL) {
	*InstancePtr->RecvBufferPtr++ =
	(u8)Data;
	}
	} else if (DataWidth ==
	XSP_DATAWIDTH_HALF_WORD) {
	/*
	* Data Transfer Width is Half Word
	* (16 bit).
	*/
	if (InstancePtr->RecvBufferPtr != NULL){
	*(u16 *)InstancePtr->RecvBufferPtr =
	(u16)Data;
	InstancePtr->RecvBufferPtr += 2;
	}
	} else if (DataWidth == XSP_DATAWIDTH_WORD) {
	/*
	* Data Transfer Width is Word (32 bit).
	*/
	if (InstancePtr->RecvBufferPtr != NULL){
	*(u32 *)InstancePtr->RecvBufferPtr =
	Data;
	InstancePtr->RecvBufferPtr += 4;
	}
	}
	InstancePtr->Stats.BytesTransferred +=
	(DataWidth >> 3);
	ByteCount -= (DataWidth >> 3);
	StatusReg = XSpi_GetStatusReg(InstancePtr);
	}

As this function does not mandate the parameter ByteCount to be divisible by {1, 2, 4}-byte. It is possible that the caller can pass something like 5-byte to transmit/receive. If this is the case, then, when ByteCount (remaining bytes to receive) is nearing zero, and the DataWidth is not of XSP_DATAWIDTH_BYTE, a read can potentially consumes invalid byte(s).

Instead, would it be more robust to do something like "always test the remaining bytes to receive, and switch to XSP_DATAWIDTH_BYTE when ByteCount is less than the preset DataWidth" ? Or, we should simply add a "divisible by {1, 2, 4}-byte" check at function prologue?