linux-kernel - Re: [RFC 02/11] i2c: add quirk checks to core

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Date:	Mon, 12 Jan 2015 10:58:47 +0100
From:	Ludovic Desroches <ludovic.desroches@...el.com>
To:	Wolfram Sang <wsa@...-dreams.de>
CC:	<linux-i2c@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-mips@...ux-mips.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Ludovic Desroches <ludovic.desroches@...el.com>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [RFC 02/11] i2c: add quirk checks to core

Hi Wolfram,

On Fri, Jan 09, 2015 at 06:21:32PM +0100, Wolfram Sang wrote:
> Let the core do the checks if HW quirks prevent a transfer. Saves code
> from drivers and adds consistency.
> 
> Signed-off-by: Wolfram Sang <wsa@...-dreams.de>
> ---
>  drivers/i2c/i2c-core.c | 53 ++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 53 insertions(+)
> 
> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> index 39d25a8cb1ad..7b10a19abf5b 100644
> --- a/drivers/i2c/i2c-core.c
> +++ b/drivers/i2c/i2c-core.c
> @@ -2063,6 +2063,56 @@ module_exit(i2c_exit);
>   * ----------------------------------------------------
>   */
>  
> +/* Check if val is exceeding the quirk IFF quirk is non 0 */
> +#define i2c_quirk_exceeded(val, quirk) ((quirk) && ((val) > (quirk)))
> +
> +static int i2c_quirk_error(struct i2c_adapter *adap, struct i2c_msg *msg, char *err_msg)
> +{
> +	dev_err(&adap->dev, "quirk: %s (addr 0x%04x, size %u)\n", err_msg, msg->addr, msg->len);
> +	return -EOPNOTSUPP;
> +}
> +
> +static int i2c_check_for_quirks(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
> +{
> +	struct i2c_adapter_quirks *q = adap->quirks;
> +	u16 max_read = q->max_read_len, max_write = q->max_write_len;
> +	int max_num = q->max_num_msgs, i;
> +
> +	if (q->flags & I2C_ADAPTER_QUIRK_COMB_WRITE_THEN_READ)
> +		max_num = 2;
> +
> +	if (i2c_quirk_exceeded(num, max_num))
> +		return i2c_quirk_error(adap, &msgs[0], "too many messages");
> +
> +	if (num == 2 && q->flags & I2C_ADAPTER_QUIRK_COMB_WRITE_FIRST) {
> +		if (msgs[0].flags & I2C_M_RD)
> +			return i2c_quirk_error(adap, &msgs[0], "invalid first write msg");
> +
> +		max_write = q->max_comb_write_len;
> +	}
> +
> +	if (num == 2 && q->flags & I2C_ADAPTER_QUIRK_COMB_READ_SECOND) {
> +		if (!(msgs[1].flags & I2C_M_RD) || msgs[0].addr != msgs[1].addr)
> +			return i2c_quirk_error(adap, &msgs[1], "invalid second read msg");
> +
> +		max_read = q->max_comb_read_len;
> +	}
> +
> +	for (i = 0; i < num; i++) {
> +		u16 len = msgs[i].len;
> +
> +		if (msgs[i].flags & I2C_M_RD) {
> +			if (i2c_quirk_exceeded(len, max_read))
> +				return i2c_quirk_error(adap, &msgs[i], "msg too long");
> +		} else {
> +			if (i2c_quirk_exceeded(len, max_write))
> +				return i2c_quirk_error(adap, &msgs[i], "msg too long");
> +		}
> +	}
> +

I am not sure it will perfectly fit at91 quirks.

The hardware can handle two messages by using the internal address
feature. The internal address size is from one byte to three bytes. Then
the length of the first message is limited to three but we don't have
this constraint for the second one. If we have 'write then read' no problem
but if we have two write messages, the second one will cause a quirk
exceeded error.

Regards

Ludovic

> +	return 0;
> +}
> +
>  /**
>   * __i2c_transfer - unlocked flavor of i2c_transfer
>   * @adap: Handle to I2C bus
> @@ -2080,6 +2130,9 @@ int __i2c_transfer(struct i2c_adapter *adap, struct i2c_msg *msgs, int num)
>  	unsigned long orig_jiffies;
>  	int ret, try;
>  
> +	if (adap->quirks && i2c_check_for_quirks(adap, msgs, num))
> +		return -EOPNOTSUPP;
> +
>  	/* i2c_trace_msg gets enabled when tracepoint i2c_transfer gets
>  	 * enabled.  This is an efficient way of keeping the for-loop from
>  	 * being executed when not needed.
> -- 
> 2.1.3
> 
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