Subject: [linux-sunxi] Re: [PATCH v2 5/5] simplefb: add clock handling code

From: [email-masked] (Hans de Goede)
Date: Mon, 06 Oct 2014 11:11:44 +0200

Hi,

On 10/06/2014 10:55 AM, Maxime Ripard wrote:
> Hi,
> 
> On Fri, Oct 03, 2014 at 01:52:05PM +0200, Hans de Goede wrote:
>> From: Luc Verhaegen <[email-masked]>
>>
>> This claims and enables clocks listed in the simple framebuffer dt node.
>> This is needed so that the display engine, in case the required clocks
>> are known by the kernel code and are described in the dt, will remain
>> properly enabled.
>>
>> Signed-off-by: Luc Verhaegen <[email-masked]>
>> [hdegoede at redhat.com: drop dev_err on kzalloc failure]
>> Reviewed-by: Hans de Goede <[email-masked]>
>> Signed-off-by: Hans de Goede <[email-masked]>
>> ---
>>  drivers/video/fbdev/simplefb.c | 100 ++++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 98 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/video/fbdev/simplefb.c b/drivers/video/fbdev/simplefb.c
>> index b7d5c08..f329cc1 100644
>> --- a/drivers/video/fbdev/simplefb.c
>> +++ b/drivers/video/fbdev/simplefb.c
>> @@ -26,6 +26,7 @@
>>  #include <linux/module.h>
>>  #include <linux/platform_data/simplefb.h>
>>  #include <linux/platform_device.h>
>> +#include <linux/clk-provider.h>
>>  
>>  static struct fb_fix_screeninfo simplefb_fix = {
>>  	.id		= "simple",
>> @@ -165,8 +166,98 @@ static int simplefb_parse_pd(struct platform_device *pdev,
>>  	return 0;
>>  }
>>  
>> +/*
>> + * Clock handling code.
>> + *
>> + * Here we handle the clocks property of our "simple-framebuffer" dt node.
>> + * This is necessary so that we can make sure that any clocks needed by
>> + * the display engine that the bootloader set up for us (and for which it
>> + * provided a simplefb dt node), stay up, for the life of the simplefb
>> + * driver.
>> + *
>> + * When the driver unloads, we cleanly disable, and then release the clocks.
>> + */
>> +struct simplefb_clock {
>> +	struct list_head list;
>> +	struct clk *clock;
>> +};
>> +
>> +/*
>> + * We only complain about errors here, no action is taken as the most likely
>> + * error can only happen due to a mismatch between the bootloader which set
>> + * up simplefb, and the clock definitions in the device tree. Chances are
>> + * that there are no adverse effects, and if there are, a clean teardown of
>> + * the fb probe will not help us much either. So just complain and carry on,
>> + * and hope that the user actually gets a working fb at the end of things.
>> + */
>> +static void
>> +simplefb_clocks_init(struct platform_device *pdev, struct list_head *list)
>> +{
>> +	struct device_node *np = pdev->dev.of_node;
>> +	int clock_count, i;
>> +
>> +	INIT_LIST_HEAD(list);
>> +
>> +	if (dev_get_platdata(&pdev->dev) || !np)
>> +		return;
>> +
>> +	clock_count = of_clk_get_parent_count(np);
> 
> This looks like it does what you expect, but its name and the fact
> that it's in the clk-provider.h file makes me wonder if you're not
> using the wrong side of the abstraction.

I'll check to see if there is something better, assuming Luc does not
beat me to it.

> 
>> +	for (i = 0; i < clock_count; i++) {
>> +		struct simplefb_clock *entry;
>> +		struct clk *clock = of_clk_get(np, i);
> 
> devm_clk_get?

Yes that would be better.

>> +		int ret;
>> +
>> +		if (IS_ERR(clock)) {
>> +			dev_err(&pdev->dev, "%s: clock %d not found: %ld\n",
>> +			       __func__, i, PTR_ERR(clock));
>> +			continue;
>> +		}
>> +
>> +		ret = clk_prepare_enable(clock);
>> +		if (ret) {
>> +			dev_err(&pdev->dev,
>> +				"%s: failed to enable clock %d: %d\n",
>> +			       __func__, i, ret);
>> +			clk_put(clock);
>> +			continue;
>> +		}
>> +
>> +		entry = kzalloc(sizeof(struct simplefb_clock), GFP_KERNEL);
>> +		if (!entry) {
>> +			clk_disable_unprepare(clock);
>> +			clk_put(clock);
>> +			continue;
>> +		}
>> +
>> +		entry->clock = clock;
>> +		/*
>> +		 * add to the front of the list, so we disable clocks in the
>> +		 * correct order.
>> +		 */
>> +		list_add(&entry->list, list);
> 
> I really don't think this whole list dance is necessary, especially
> after reading this comment. 

So you're suggesting to just make this an array, with say 5 entries, or ... ?

Regards,

Hans