linux-kernel - Re: [PATCH v2 3/4] Coresight: Add Coresight Control Unit driver

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Message-ID: <Zoy3FwurfmQUhF0S@jiegan-gv.ap.qualcomm.com>
Date: Tue, 9 Jul 2024 12:05:43 +0800
From: JieGan <quic_jiegan@...cinc.com>
To: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
CC: Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose
	<suzuki.poulose@....com>,
        Alexander Shishkin
	<alexander.shishkin@...ux.intel.com>,
        Mike Leach <mike.leach@...aro.org>, "Rob Herring" <robh+dt@...nel.org>,
        Krzysztof Kozlowski
	<krzysztof.kozlowski+dt@...aro.org>,
        James Clark <james.clark@....com>,
        Jinlong Mao <quic_jinlmao@...cinc.com>, Leo Yan <leo.yan@...aro.org>,
        <coresight@...ts.linaro.org>, <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        Tingwei Zhang
	<quic_tingweiz@...cinc.com>,
        Yuanfang Zhang <quic_yuanfang@...cinc.com>,
        "Tao
 Zhang" <quic_taozha@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        "Song
 Chai" <quic_songchai@...cinc.com>,
        <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] Coresight: Add Coresight Control Unit driver

On Mon, Jul 08, 2024 at 12:44:43PM +0200, Krzysztof Kozlowski wrote:
> On 08/07/2024 05:16, JieGan wrote:
> > 
> >>
> >>> +
> >>> +	drvdata->base = devm_ioremap(dev, res->start, resource_size(res));
> >>
> >> Use proper wrapper for this two.
> > Replaced by:
> > res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > drvdata->base = devm_ioremap_resource(dev, res);
> 
> Why?
> 
> Use the wrapper.
Sorry, I misunderstood the "wrapper" before.
Just wrapped drvdata->base by void __iomem *base;

> 
> 
> ...
> 
> >>> +
> >>> +static struct platform_driver ccu_driver = {
> >>> +	.probe          = ccu_probe,
> >>> +	.remove         = ccu_remove,
> >>> +	.driver         = {
> >>> +		.name   = "coresight-ccu",
> >>> +		.of_match_table = ccu_match,
> >>> +		.suppress_bind_attrs = true,
> >>
> >> Why?
> > Sorry, I dont get the point here.
> 
> You do not get the point why I am asking "why?"?
> 
> Why do you need it?
> 
> > We dont need automatic bind/unbind, so the suppress_bind_attrs sets to true.
> 
> But I need it...
> 
> > We need configure some settings before we register the device.
> 
> Hm, is this expected for coresight devices?
The coresight device cannot be unbinded independently. As we known, 
The coresight devices collaborate to form a path, from source, link, to sink.
If an unexpected unbinding occurs for a coresight device that is part of the path,
it will disrupt the entire path.

I think it's the reason why the coresight device driver does not need automatic bind/unbind.
Here is the previous discussion for suppress_bind_attrs:
https://lore.kernel.org/all/1453753248-1716-1-git-send-email-mathieu.poirier@linaro.org/#r

> 
> Best regards,
> Krzysztof
> 

Thanks,
Jie