linux-kernel - Re: [PATCH v4 2/3] hwrng: add Rockchip SoC hwrng driver

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Date: Sun, 23 Jun 2024 13:47:47 +0200
From: Dragan Simic <dsimic@...jaro.org>
To: Uwe Kleine-König <ukleinek@...ian.org>
Cc: Krzysztof Kozlowski <krzk@...nel.org>, Daniel Golle
 <daniel@...rotopia.org>, Aurelien Jarno <aurelien@...el32.net>, Olivia
 Mackall <olivia@...enic.com>, Herbert Xu <herbert@...dor.apana.org.au>, Rob
 Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor
 Dooley <conor+dt@...nel.org>, Heiko Stuebner <heiko@...ech.de>, Philipp
 Zabel <p.zabel@...gutronix.de>, Sebastian Reichel
 <sebastian.reichel@...labora.com>, Sascha Hauer <s.hauer@...gutronix.de>,
 Martin Kaiser <martin@...ser.cx>, Ard Biesheuvel <ardb@...nel.org>,
 linux-crypto@...r.kernel.org, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/3] hwrng: add Rockchip SoC hwrng driver

Hello Uwe,

On 2024-06-23 11:46, Uwe Kleine-König wrote:
> On 6/23/24 09:00, Krzysztof Kozlowski wrote:
>> On 23/06/2024 05:33, Daniel Golle wrote:
>>> +
>>> +	pm_runtime_set_autosuspend_delay(dev, RK_RNG_AUTOSUSPEND_DELAY);
>>> +	pm_runtime_use_autosuspend(dev);
>>> +	devm_pm_runtime_enable(dev);
>>> +
>>> +	ret = devm_hwrng_register(dev, &rk_rng->rng);
>>> +	if (ret)
>>> +		return dev_err_probe(&pdev->dev, ret, "Failed to register Rockchip 
>>> hwrng\n");
>>> +
>>> +	dev_dbg(&pdev->dev, "Registered Rockchip hwrng\n");
>> 
>> Drop, it is not useful at all. Srsly, we had already long enough talk,
>> [...]
> 
> And in this long talk using dev_dbg() was one of the suggestions for a
> compromise. For me this is ok.
> 
>> There is no single benefit of such debug statement. sysfs already
>> provides you this information. Simple entry/exit  is provided by
>> tracing. You duplicate existing interfaces without any benefit, 
>> because
>> this prints nothing more.
> 
> There might be a (small) value if you want to know when during boot
> the device becomes available. So having a dev_dbg() that can be
> enabled dynamically (assuming DYNAMIC_DEBUG=y) and isn't in the way
> otherwise might be justified. IMHO a dev_dbg is lightweight enough
> that *I* won't continue the discussion.

For anyone interested, below is an example that shows the usability
of knowing when a device becomes available:

https://gitlab.manjaro.org/manjaro-arm/packages/core/linux/-/issues/21