linux-kernel - Re: [PATCH 02/10] i2c: xiic: Add standard mode support for

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Date:   Wed, 2 Jun 2021 13:17:10 +0200
From:   Marek Vasut <marex@...x.de>
To:     Raviteja Narayanam <raviteja.narayanam@...inx.com>,
        linux-i2c@...r.kernel.org, michal.simek@...inx.com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        git@...inx.com
Subject: Re: [PATCH 02/10] i2c: xiic: Add standard mode support for > 255 byte
 read transfers

On 5/31/21 3:19 PM, Raviteja Narayanam wrote:

[...]

> +	if (i2c->dynamic) {
> +		u8 bytes;
> +		u16 val;
> +
> +		/* Clear and enable Rx full interrupt. */
> +		xiic_irq_clr_en(i2c, XIIC_INTR_RX_FULL_MASK |
> +				XIIC_INTR_TX_ERROR_MASK);
> +
> +		/*
> +		 * We want to get all but last byte, because the TX_ERROR IRQ
> +		 * is used to indicate error ACK on the address, and
> +		 * negative ack on the last received byte, so to not mix
> +		 * them receive all but last.
> +		 * In the case where there is only one byte to receive
> +		 * we can check if ERROR and RX full is set at the same time
> +		 */
> +		rx_watermark = msg->len;
> +		bytes = min_t(u8, rx_watermark, IIC_RX_FIFO_DEPTH);
> +		bytes--;
> +
> +		xiic_setreg8(i2c, XIIC_RFD_REG_OFFSET, bytes);
> +
> +		local_irq_save(flags);
> +		if (!(msg->flags & I2C_M_NOSTART))
> +			/* write the address */
> +			xiic_setreg16(i2c, XIIC_DTR_REG_OFFSET,
> +				      i2c_8bit_addr_from_msg(msg) |
> +				      XIIC_TX_DYN_START_MASK);
> +
> +		xiic_irq_clr_en(i2c, XIIC_INTR_BNB_MASK);
> +
> +		/* If last message, include dynamic stop bit with length */
> +		val = (i2c->nmsgs == 1) ? XIIC_TX_DYN_STOP_MASK : 0;
> +		val |= msg->len;
> +
> +		xiic_setreg16(i2c, XIIC_DTR_REG_OFFSET, val);
> +		local_irq_restore(flags);

Is local_irq_save()/local_irq_restore() used here to prevent concurrent 
access to the XIIC ?

[...]