linux-kernel - Re: [PATCH v7 2/4] i2c: npcm: Modify the client address assignment

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Message-ID: <kzsvr3jepoqjahn7n2jch5vrqim5eknylrasvsbjugfhzny46o@bemfk6knfmxi>
Date: Thu, 24 Oct 2024 12:03:57 +0200
From: Andi Shyti <andi.shyti@...nel.org>
To: Tyrone Ting <warp5tw@...il.com>
Cc: avifishman70@...il.com, tmaimon77@...il.com, tali.perry1@...il.com, 
	venture@...gle.com, yuenn@...gle.com, benjaminfair@...gle.com, 
	andriy.shevchenko@...ux.intel.com, wsa@...nel.org, rand.sec96@...il.com, 
	wsa+renesas@...g-engineering.com, tali.perry@...oton.com, Avi.Fishman@...oton.com, 
	tomer.maimon@...oton.com, KWLIU@...oton.com, JJLIU0@...oton.com, kfting@...oton.com, 
	openbmc@...ts.ozlabs.org, linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 2/4] i2c: npcm: Modify the client address assignment

Hi Tyrone,

...

> +	/*
> +	 * Previously, the 7-bit address was stored and being converted to
> +	 * the address of event in the following call to npcm_i2c_master_start_xmit().

Do we care how it was done previously? I think this is not a
useful information as the code readers will se the code the way
it is now, not the way it was done "previously".

(there is a related comment at the end)

> +	 * Since there are cases that the i2c_recover_bus() gets called at the
> +	 * early stage of npcm_i2c_master_xfer(), the address of event is stored
> +	 * and then used in the i2c_recover_bus().

I could rephrase this sentence to something like:

/*
 * Store the address early in a global position to ensure it is
 * accessible for a potential call to i2c_recover_bus().
 */

> +	 */
> +	bus->dest_addr = i2c_8bit_addr_from_msg(msg0);
> +
>  	/*
>  	 * Check the BER (bus error) state, when ber_state is true, it means that the module
>  	 * detects the bus error which is caused by some factor like that the electricity
> @@ -2165,6 +2175,15 @@ static int npcm_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
>  	 * bus is busy.
>  	 */
>  	if (bus_busy || bus->ber_state) {
> +		/*
> +		 * Since the transfer might be a read operation, remove the I2C_M_RD flag
> +		 * from the bus->dest_addr for the i2c_recover_bus() call later.
> +		 *
> +		 * The i2c_recover_bus() uses the address in a write direction to recover
> +		 * the i2c bus if some error condition occurs.
> +		 */
> +		bus->dest_addr &= ~I2C_M_RD;
> +
>  		iowrite8(NPCM_I2CCST_BB, bus->reg + NPCM_I2CCST);
>  		npcm_i2c_reset(bus);
>  		i2c_recover_bus(adap);
> @@ -2172,7 +2191,6 @@ static int npcm_i2c_master_xfer(struct i2c_adapter *adap, struct i2c_msg *msgs,
>  	}
>  
>  	npcm_i2c_init_params(bus);
> -	bus->dest_addr = slave_addr;

We can now get rid of slave_addr. It's just used in
npcm_i2c_master_start_xmit(). Right?

Andi

>  	bus->msgs = msgs;
>  	bus->msgs_num = num;
>  	bus->cmd_err = 0;
> -- 
> 2.34.1
>