On Fri, May 11, 2018 at 01:38:21PM +0300, Radu Pirea wrote:

> +config SPI_AT91_USART
> +        tristate "Atmel USART Controller as SPI"
> +     depends on HAS_DMA
> +     depends on (ARCH_AT91 || COMPILE_TEST)
> +        select MFD_AT91_USART
> +     help
> +       This selects a driver for the AT91 USART Controller as SPI Master,
> +       present on AT91 and SAMA5 SoC series.
> +

This looks like there's some tab/space mixing going on here.

> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Driver for AT91 USART Controllers as SPI
> + *
> + * Copyright (C) 2018 Microchip Technology Inc.

Make the entire block a C++ comment so it looks more intentional rather
tha mixing C and C++.

> +static inline void at91_usart_spi_tx(struct at91_usart_spi *aus)
> +{
> +     unsigned int len = aus->current_transfer->len;
> +     unsigned int remaining = aus->current_tx_remaining_bytes;
> +     const u8  *tx_buf = aus->current_transfer->tx_buf;
> +
> +     if (tx_buf && remaining) {
> +             if (at91_usart_spi_tx_ready(aus))
> +                     spi_writel(aus, THR, tx_buf[len - remaining]);
> +                     aus->current_tx_remaining_bytes--;

Missing braces here - we only write to the FIFO if there's space but we
unconditionally decrement the counter.

> +     } else {
> +             if (at91_usart_spi_tx_ready(aus))
> +                     spi_writel(aus, THR, US_DUMMY_TX);
> +     }
> +}

This looks like you're open coding SPI_CONTROLLER_MUST_TX

> +     int len = aus->current_transfer->len;
> +     int remaining = aus->current_rx_remaining_bytes;
> +     u8  *rx_buf = aus->current_transfer->rx_buf;
> +
> +     if (aus->current_rx_remaining_bytes) {
> +             rx_buf[len - remaining] = spi_readb(aus, RHR);
> +             aus->current_rx_remaining_bytes--;
> +     } else {
> +             spi_readb(aus, RHR);
> +     }

Similarly for _MUST_RX.

> +     controller->flags = SPI_MASTER_MUST_RX | SPI_MASTER_MUST_TX;

You're actually setting both flags...  this means that the handling for
cases with missing TX or RX buffers can't happen.

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