linux-kernel - Re: [PATCH v2 5/5] fbdev/simplefb: Add support for interconnect paths

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Message-Id: <DAX814DZF6AT.31N8TZWL5LMDT@fairphone.com>
Date: Fri, 27 Jun 2025 11:51:09 +0200
From: "Luca Weiss" <luca.weiss@...rphone.com>
To: "Javier Martinez Canillas" <javierm@...hat.com>, "Hans de Goede"
 <hdegoede@...hat.com>, "Maarten Lankhorst"
 <maarten.lankhorst@...ux.intel.com>, "Maxime Ripard" <mripard@...nel.org>,
 "Thomas Zimmermann" <tzimmermann@...e.de>, "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>, "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 v2 5/5] fbdev/simplefb: Add support for interconnect
 paths

On Fri Jun 27, 2025 at 9:56 AM CEST, Javier Martinez Canillas wrote:
> Luca Weiss <luca.weiss@...rphone.com> writes:
>
>> 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.
>>
>> Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
>> Signed-off-by: Luca Weiss <luca.weiss@...rphone.com>
>> ---
>>  drivers/video/fbdev/simplefb.c | 83 ++++++++++++++++++++++++++++++++++++++++++
>>  1 file changed, 83 insertions(+)
>>
>
> [...]
>
>> +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
>
> These two functions contain the same logic that you are using in the
> simpledrm driver. I wonder if could be made helpers so that the code
> isn't duplicated in both drivers.

I believe most resource handling code (clocks, regulators,
power-domains, plus now interconnect) should be pretty generic between
the two.

>
> But in any case it could be a follow-up of your series I think.

To be fair, I don't think I'll work on this, I've got plenty of Qualcomm
SoC-specific bits to work on :)

Regards
Luca

>
> Reviewed-by: Javier Martinez Canillas <javierm@...hat.com>