linux-kernel - Re: [PATCH 3/3] fbdev/simplefb: Add support for interconnect paths

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Message-Id: <DARBA03BEQA1.3KLHCBFNTVXKJ@fairphone.com>
Date: Fri, 20 Jun 2025 13:07:49 +0200
From: "Luca Weiss" <luca.weiss@...rphone.com>
To: "Thomas Zimmermann" <tzimmermann@...e.de>, "Hans de Goede"
 <hdegoede@...hat.com>, "Maarten Lankhorst"
 <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard" <mripard@...nel.org>,
 "David Airlie" <airlied@...il.com>, "Simona Vetter" <simona@...ll.ch>, "Rob
 Herring" <robh@...nel.org>, "Krzysztof Kozlowski" <krzk+dt@...nel.org>,
 "Conor Dooley" <conor+dt@...nel.org>, "Javier Martinez Canillas"
 <javierm@...hat.com>, "Helge Deller" <deller@....de>
Cc: <linux-fbdev@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
 <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] fbdev/simplefb: Add support for interconnect paths

Hi Thomas,

On Fri Jun 20, 2025 at 1:02 PM CEST, Thomas Zimmermann wrote:
> Hi
>
> Am 20.06.25 um 12:31 schrieb Luca Weiss:
>> Some devices might require keeping an interconnect path alive so that
>> the framebuffer continues working. Add support for that by setting the
>> bandwidth requirements appropriately for all provided interconnect
>> paths.
>>
>> Signed-off-by: Luca Weiss <luca.weiss@...rphone.com>
>> ---
>>   drivers/video/fbdev/simplefb.c | 83 ++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 83 insertions(+)
>>
>> diff --git a/drivers/video/fbdev/simplefb.c b/drivers/video/fbdev/simplefb.c
>> index be95fcddce4c8ca794826b805cd7dad2985bd637..ca73e079fd13550ddc779e84db80f7f9b743d074 100644
>> --- a/drivers/video/fbdev/simplefb.c
>> +++ b/drivers/video/fbdev/simplefb.c
>> @@ -27,6 +27,7 @@
>>   #include <linux/parser.h>
>>   #include <linux/pm_domain.h>
>>   #include <linux/regulator/consumer.h>
>> +#include <linux/interconnect.h>
>
> With alphabetical sorting:
>
> Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>

Thanks for the reviews!

For both simpledrm.c and simplefb.c, the includes are not strictly
alphabetically sorted (1 mis-sort in simpledrm, 3 in simplefb), shall I
just try and slot it into the best fitting place, or make them sorted in
my patch? Or I can add a separate commit for each driver before to sort
them.

Let me know!

Regards
Luca


>
> Best regards
> Thomas
>
>
>>   
>>   static const struct fb_fix_screeninfo simplefb_fix = {
>>   	.id		= "simple",
>> @@ -89,6 +90,10 @@ struct simplefb_par {
>>   	u32 regulator_count;
>>   	struct regulator **regulators;
>>   #endif
>> +#if defined CONFIG_OF && defined CONFIG_INTERCONNECT
>> +	unsigned int icc_count;
>> +	struct icc_path **icc_paths;
>> +#endif
>>   };
>>   
>>   static void simplefb_clocks_destroy(struct simplefb_par *par);
>> @@ -525,6 +530,80 @@ static int simplefb_attach_genpds(struct simplefb_par *par,
>>   }
>>   #endif
>>   
>> +#if defined CONFIG_OF && defined CONFIG_PM_GENERIC_DOMAINS
>> +/*
>> + * Generic interconnect path handling code.
>> + */
>> +static void simplefb_detach_icc(void *res)
>> +{
>> +	struct simplefb_par *par = res;
>> +	int i;
>> +
>> +	for (i = par->icc_count - 1; i >= 0; i--) {
>> +		if (!IS_ERR_OR_NULL(par->icc_paths[i]))
>> +			icc_put(par->icc_paths[i]);
>> +	}
>> +}
>> +
>> +static int simplefb_attach_icc(struct simplefb_par *par,
>> +			       struct platform_device *pdev)
>> +{
>> +	struct device *dev = &pdev->dev;
>> +	int ret, count, i;
>> +
>> +	count = of_count_phandle_with_args(dev->of_node, "interconnects",
>> +							 "#interconnect-cells");
>> +	if (count < 0)
>> +		return 0;
>> +
>> +	/* An interconnect path consists of two elements */
>> +	if (count % 2) {
>> +		dev_err(dev, "invalid interconnects value\n");
>> +		return -EINVAL;
>> +	}
>> +	par->icc_count = count / 2;
>> +
>> +	par->icc_paths = devm_kcalloc(dev, par->icc_count,
>> +				      sizeof(*par->icc_paths),
>> +				      GFP_KERNEL);
>> +	if (!par->icc_paths)
>> +		return -ENOMEM;
>> +
>> +	for (i = 0; i < par->icc_count; i++) {
>> +		par->icc_paths[i] = of_icc_get_by_index(dev, i);
>> +		if (IS_ERR_OR_NULL(par->icc_paths[i])) {
>> +			ret = PTR_ERR(par->icc_paths[i]);
>> +			if (ret == -EPROBE_DEFER)
>> +				goto err;
>> +			dev_err(dev, "failed to get interconnect path %u: %d\n", i, ret);
>> +			continue;
>> +		}
>> +
>> +		ret = icc_set_bw(par->icc_paths[i], 0, UINT_MAX);
>> +		if (ret) {
>> +			dev_err(dev, "failed to set interconnect bandwidth %u: %d\n", i, ret);
>> +			continue;
>> +		}
>> +	}
>> +
>> +	return devm_add_action_or_reset(dev, simplefb_detach_icc, par);
>> +
>> +err:
>> +	while (i) {
>> +		--i;
>> +		if (!IS_ERR_OR_NULL(par->icc_paths[i]))
>> +			icc_put(par->icc_paths[i]);
>> +	}
>> +	return ret;
>> +}
>> +#else
>> +static int simplefb_attach_icc(struct simplefb_par *par,
>> +			       struct platform_device *pdev)
>> +{
>> +	return 0;
>> +}
>> +#endif
>> +
>>   static int simplefb_probe(struct platform_device *pdev)
>>   {
>>   	int ret;
>> @@ -615,6 +694,10 @@ static int simplefb_probe(struct platform_device *pdev)
>>   	if (ret < 0)
>>   		goto error_regulators;
>>   
>> +	ret = simplefb_attach_icc(par, pdev);
>> +	if (ret < 0)
>> +		goto error_regulators;
>> +
>>   	simplefb_clocks_enable(par, pdev);
>>   	simplefb_regulators_enable(par, pdev);
>>   
>>