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

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Date:   Thu, 3 Jun 2021 05:33:38 +0000
From:   Raviteja Narayanam <rna@...inx.com>
To:     Marek Vasut <marex@...x.de>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        Michal Simek <michals@...inx.com>
CC:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        git <git@...inx.com>
Subject: RE: [PATCH 02/10] i2c: xiic: Add standard mode support for > 255 byte
 read transfers

Hi Marek,

> -----Original Message-----
> From: Marek Vasut <marex@...x.de>
> Sent: Wednesday, June 2, 2021 4:47 PM
> To: Raviteja Narayanam <rna@...inx.com>; linux-i2c@...r.kernel.org; Michal
> Simek <michals@...inx.com>
> Cc: linux-arm-kernel@...ts.infradead.org; linux-kernel@...r.kernel.org; git
> <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 ?

These were used to fix the timing constraint between two register writes to the IP.
As we have discussed last time, these are removed in " [PATCH 08/10] i2c: xiic: Remove interrupt enable/disable in Rx path".
Now they are no longer needed since our IP is fixed. 
For legacy IP versions, driver is switching to 'AXI I2C standard mode' of operation in 
" [PATCH 07/10] i2c: xiic: Switch to Xiic standard mode for i2c-read".

Regards,
Raviteja N