linux-kernel - Re: [PATCH] i2c: imx: add retries for i2c-0 on Ventana boards

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Date:	Fri, 8 Jul 2016 08:28:46 +0200
From:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
To:	Tim Harvey <tharvey@...eworks.com>
Cc:	Wolfram Sang <wsa@...-dreams.de>,
	Fabio Estevam <fabio.estevam@...escale.com>,
	linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] i2c: imx: add retries for i2c-0 on Ventana boards

Hello Tim,

On Thu, Jul 07, 2016 at 07:03:49AM -0700, Tim Harvey wrote:
> Gateworks Ventana IMX6 based boards have a Gateworks System Controller [1]
> (gsc) device that can NAK i2c transactions when its busy in an ADC loop. As
> this is always on i2c-0 we will add retries for that bus for any Ventana
> board.

The right thing is to fix the drivers IMHO.

> diff --git a/drivers/i2c/busses/i2c-imx.c b/drivers/i2c/busses/i2c-imx.c
> index 1844bc9..aec71c3 100644
> --- a/drivers/i2c/busses/i2c-imx.c
> +++ b/drivers/i2c/busses/i2c-imx.c
> @@ -460,6 +460,8 @@ static int i2c_imx_acked(struct imx_i2c_struct *i2c_imx)
>  {
>  	if (imx_i2c_read_reg(i2c_imx, IMX_I2C_I2SR) & I2SR_RXAK) {
>  		dev_dbg(&i2c_imx->adapter.dev, "<%s> No ACK\n", __func__);
> +		if (i2c_imx->adapter.retries)
> +			return -EAGAIN;

This is wrong, struct i2c_adapter::retries is for restarting a transfer
on arbitration loss.

>  		return -ENXIO;  /* No ACK */
>  	}
>  
> @@ -1068,6 +1070,16 @@ static int i2c_imx_probe(struct platform_device *pdev)
>  	i2c_imx->adapter.dev.of_node	= pdev->dev.of_node;
>  	i2c_imx->base			= base;
>  
> +	/*
> +	 * The Gateworks Ventana has an i2c based system controller on i2c-0
> +	 * which emulates several standard i2c devices with existing drivers.
> +	 * That device can NAK when its in an ADC loop. Add bus retries.
> +	 */
> +	if (of_machine_is_compatible("gw,ventana") && phy_addr == 0x021a0000) {

Please don't. If you want to do handle a device in a special way, invent
a device tree property, add it to your machine description and add
handling here. Using of_machine_is_compatible + base address of the
device to decide about configuration is a no go.

> +		dev_info(&pdev->dev, "Adding retries for Ventana GSC\n");
> +		i2c_imx->adapter.retries = 3;
> +	}
> +

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |