linux-kernel - Re: [PATCH V2] i2c-designware: Add Intel Baytrail PMIC I2C bus support

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Date:	Tue, 11 Nov 2014 12:32:56 +0100
From:	Wolfram Sang <wsa@...-dreams.de>
To:	"David E. Box" <david.e.box@...ux.intel.com>
Cc:	jdelvare@...e.de, arnd@...db.de, maxime.ripard@...e-electrons.com,
	dianders@...omium.org, u.kleine-koenig@...gutronix.de,
	laurent.pinchart+renesas@...asonboard.com,
	boris.brezillon@...e-electrons.com, maxime.coquelin@...com,
	andrew@...n.ch, sjg@...omium.org, markus.mayer@...aro.org,
	ch.naveen@...sung.com, jacob.jun.pan@...ux.intel.com,
	max.schwarz@...ine.de, mika.westerberg@...ux.intel.com,
	skuribay@...ox.com, Romain.Baeriswyl@...lis.com,
	wenkai.du@...el.com, chiau.ee.chew@...el.com,
	christian.ruppert@...lis.com, alan@...ux.intel.com,
	linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH V2] i2c-designware: Add Intel Baytrail PMIC I2C bus
 support

On Tue, Sep 23, 2014 at 11:40:26AM -0700, David E. Box wrote:
> This patch implements an I2C bus sharing mechanism between the host and platform
> hardware on select Intel BayTrail SoC platforms using the X-Powers AXP288 PMIC.
> 
> On these platforms access to the PMIC must be shared with platform hardware. The
> hardware unit assumes full control of the I2C bus and the host must request
> access through a special semaphore. Hardware control of the bus also makes it
> necessary to disable runtime pm to avoid interfering with hardware transactions.

Can we foresee that other platforms will have similar mechanisms in the
future?

> +config I2C_BAYTRAIL_SEM

I2C_DESIGNWARE_BAYTRAIL_SEM

> +	tristate "Intel Baytrail I2C semaphore support"
> +	depends on I2C_DESIGNWARE_PLATFORM
> +	select I2C_DESIGNWARE_CORE

This select is already covered by I2C_DESIGNWARE_PLATFORM.

> +	select IOSF_MBI
> +	help
> +	  This driver enables host access to the PMIC I2C bus on select Intel
> +	  BayTrail platforms using the X-Powers AXP288 PMIC. This driver is
> +	  required for host access to the PMIC on these platforms. You should
> +	  probably say Y if you have a BayTrail system, unless you know it uses
> +	  a different PMIC. Otherwises critical PMIC functions, like charging,
> +	  may not operate.
> +
> +	  This driver should be built as a m if I2C_DESIGNWARE_PLATFORM=m,
> +	  and as y if I2C_DESIGNWARE_PLATFORM=y.

That shouldn't be the user's task to ensure. Please enforce this in the
makefile. Check Documentation/kbuid/makefiles.txt, Section 3.3.

> --- /dev/null
> +++ b/drivers/i2c/busses/i2c-baytrail-sem.c
> @@ -0,0 +1,157 @@
> +/*
> + * Intel BayTrail PMIC I2C bus semaphore implementaion
> + * Copyright (c) 2014, Intel Corporation.

Mika, can you have a look at the ACPI part here?

> diff --git a/drivers/i2c/busses/i2c-designware-core.h b/drivers/i2c/busses/i2c-designware-core.h
> index d66b6cb..13e0809 100644
> --- a/drivers/i2c/busses/i2c-designware-core.h
> +++ b/drivers/i2c/busses/i2c-designware-core.h
> @@ -65,6 +65,8 @@
>   * @ss_lcnt: standard speed LCNT value
>   * @fs_hcnt: fast speed HCNT value
>   * @fs_lcnt: fast speed LCNT value
> + * has_hw_lock: true if bus access requires hardware lock
> + * pm_runtime_disabled: true if pm runtime is disabled

Look closely. There is a difference to the entries above.

> @@ -123,3 +127,18 @@ extern void i2c_dw_disable(struct dw_i2c_dev *dev);
>  extern void i2c_dw_clear_int(struct dw_i2c_dev *dev);
>  extern void i2c_dw_disable_int(struct dw_i2c_dev *dev);
>  extern u32 i2c_dw_read_comp_param(struct dw_i2c_dev *dev);
> +
> +#if IS_ENABLED(CONFIG_I2C_BAYTRAIL_SEM)
> +extern int baytrail_i2c_acquire(struct dw_i2c_dev *dev);
> +extern void baytrail_i2c_release(struct dw_i2c_dev *dev);
> +extern void baytrail_evaluate_sem(struct dw_i2c_dev *dev);
> +#define i2c_dw_acquire_ownership(dev) baytrail_i2c_acquire(dev)
> +#define i2c_dw_release_ownership(dev) baytrail_i2c_release(dev)
> +#define i2c_dw_eval_lock(dev) baytrail_evaluate_sem(dev)
i2c_dw_test_ownership_support()?

That doesn't scale in case other platformts will need this. I could
imagine a struct i2c_dw_ownership_ops() (or whatever name) which gets
populated according to the matched device.

Thanks,

   Wolfram


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