Message-ID: <519C6459.7000604@ti.com>
Date: Wed, 22 May 2013 11:53:21 +0530
From: Kishon Vijay Abraham I <kishon@ti.com>
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To: "myungjoo.ham" <myungjoo.ham@samsung.com>,
        Graeme Gregory <gg@slimlogic.co.uk>
CC: <cw00.choi@samsung.com>, <balbi@ti.com>, <ldewangan@nvidia.com>,
        <devicetree-discuss@lists.ozlabs.org>, <linux-doc@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <grant.likely@linaro.org>,
        <rob.herring@calxeda.com>, <rob@landley.net>, <ruchika@ti.com>,
        <tony@atomide.com>, <sameo@linux.intel.com>,
        <broonie@opensource.wolfsonmicro.com>
Subject: Re: [PATCH v4] extcon: Palmas Extcon Driver
References: <1362662506-14823-4-git-send-email-kishon@ti.com> <1367846225-15685-1-git-send-email-kishon@ti.com> <005c01ce4abb$d956fea0$8c04fbe0$@samsung.com> <51888F45.4030303@ti.com>
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Hi,

On Tuesday 07 May 2013 10:51 AM, Kishon Vijay Abraham I wrote:
> Hi,
>
> On Tuesday 07 May 2013 06:13 AM, myungjoo.ham wrote:
>>> From: Graeme Gregory <gg@slimlogic.co.uk>
>>>
>>> This is the driver for the USB comparator built into the palmas chip. It
>>> handles the various USB OTG events that can be generated by cable
>>> insertion/removal.
>>>
>>> Signed-off-by: Graeme Gregory <gg@slimlogic.co.uk>
>>> Signed-off-by: Moiz Sonasath <m-sonasath@ti.com>
>>> Signed-off-by: Ruchika Kharwar <ruchika@ti.com>
>>> Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
>>> [kishon@ti.com: adapted palmas usb driver to use the extcon framework]
>>> Signed-off-by: Sebastien Guiriec <s-guiriec@ti.com>
>>
>> Here goes some comments in the code:
>>
>> []
>>
>>> diff --git a/drivers/extcon/extcon-palmas.c
>> b/drivers/extcon/extcon-palmas.c
>>> new file mode 100644
>>> index 0000000..3ef042f
>>> --- /dev/null
>>> +++ b/drivers/extcon/extcon-palmas.c
>>> @@ -0,0 +1,389 @@
>>> +/*
>>> + * Palmas USB transceiver driver
>>> + *
>>> + * Copyright (C) 2013 Texas Instruments Incorporated -
>>> http://www.ti.com
>>> + * This program is free software; you can redistribute it and/or modify
>>> + * it under the terms of the GNU General Public License as published by
>>> + * the Free Software Foundation; either version 2 of the License, or
>>> + * (at your option) any later version.
>>> + *
>>> + * Author: Graeme Gregory <gg@...mlogic.co.uk>
>>> + * Author: Kishon Vijay Abraham I <kishon@...com>
>>> + *
>>> + * Based on twl6030_usb.c
>>> + *
>>> + * Author: Hema HK <hemahk@...com>
>>> + *
>>> + * This program is distributed in the hope that it will be useful,
>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>> + * GNU General Public License for more details.
>>> + */
>>
>> Why the email addresses are masked in the source code?
>> (I'm just curious as this is the first time to see such in kernel source)
>
> That was not intentional. Took the previous version from the net. My bad.
>>
>>> +
>>> +#include <linux/module.h>
>>> +#include <linux/init.h>
>>> +#include <linux/interrupt.h>
>>> +#include <linux/platform_device.h>
>>> +#include <linux/io.h>
>>> +#include <linux/usb/phy_companion.h>
>>> +#include <linux/regulator/consumer.h>
>>> +#include <linux/err.h>
>>> +#include <linux/notifier.h>
>>> +#include <linux/slab.h>
>>> +#include <linux/delay.h>
>>> +#include <linux/mfd/palmas.h>
>>> +#include <linux/of.h>
>>> +#include <linux/of_platform.h>
>>> +#include <linux/extcon/extcon_palmas.h>
>>> +
>>> +static const char *palmas_extcon_cable[] = {
>>> +    [0] = "USB",
>>> +    [1] = "USB-HOST",
>>
>>     [1] = "USB-Host",
>>
>>> +    NULL,
>>> +};
>>> +
>>> +static const int mutually_exclusive[] = {0x3, 0x0};
>>> +
>>> +static void palmas_usb_wakeup(struct palmas *palmas, int enable)
>>> +{
>>> +    if (enable)
>>> +        palmas_write(palmas, PALMAS_USB_OTG_BASE, PALMAS_USB_WAKEUP,
>>> +            PALMAS_USB_WAKEUP_ID_WK_UP_COMP);
>>> +    else
>>> +        palmas_write(palmas, PALMAS_USB_OTG_BASE, PALMAS_USB_WAKEUP,
>> 0);
>>> +}
>>> +
>>> +static ssize_t palmas_usb_vbus_show(struct device *dev,
>>> +            struct device_attribute *attr, char *buf)
>>> +{
>>> +    unsigned long        flags;
>>> +    int            ret = -EINVAL;
>>> +    struct palmas_usb    *palmas_usb = dev_get_drvdata(dev);
>>> +
>>> +    spin_lock_irqsave(&palmas_usb->lock, flags);
>>
>> This spinlock is used in this sysfs-show function only.
>> Is this really needed?
>> The only protected value here is "linkstat", which is "readonly"
>> in this protected context.
>> Thus, removing the spin_lock and updating like the following should
>> be the same with less overhead:
>>
>>     int linkstat = palmas_usb->linkstat;
>>     switch(linkstat) {
>
> hmm.. ok.
I think this is to do with disabling interrupts while reporting the VBUS 
state. (linkstat is updated in irq handler). So this should be fine I guess?

Thanks
Kishon
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