linux-kernel - Re: [RFC PATCH 1/4] drm/etnaviv: Prevent IRQ triggering at probe time on i.MX8MM

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Date:   Thu, 30 Apr 2020 15:30:06 +0000
From:   Schrempf Frieder <frieder.schrempf@...tron.de>
To:     Daniel Baluta <daniel.baluta@....com>,
        Adam Ford <aford173@...il.com>,
        Anson Huang <Anson.Huang@....com>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        Fabio Estevam <festevam@...il.com>,
        "Leonard Crestez" <leonard.crestez@....com>,
        Li Jun <jun.li@....com>, Lucas Stach <l.stach@...gutronix.de>,
        NXP Linux Team <linux-imx@....com>,
        Peng Fan <peng.fan@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        "Russell King" <linux+etnaviv@...linux.org.uk>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        "S.j. Wang" <shengjiu.wang@....com>
CC:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "etnaviv@...ts.freedesktop.org" <etnaviv@...ts.freedesktop.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH 1/4] drm/etnaviv: Prevent IRQ triggering at probe time
 on i.MX8MM

On 30.04.20 16:23, Daniel Baluta wrote:
> On 4/30/20 3:46 PM, Schrempf Frieder wrote:
>> +    /*
>> +     * On i.MX8MM there is an interrupt getting triggered immediately
>> +     * after requesting the IRQ, which leads to a stall as the handler
>> +     * accesses the GPU registers whithout the clock being enabled.
>> +     * Enabling the clocks briefly seems to clear the IRQ state, so 
>> we do
>> +     * this here before requesting the IRQ.
>> +     */
>> +    err = etnaviv_gpu_clk_enable(gpu);
>> +    if (err)
>> +        return err;
>> +
>> +    err = etnaviv_gpu_clk_disable(gpu);
>> +    if (err)
>> +        return err;
>> +
>> +    err = devm_request_irq(&pdev->dev, gpu->irq, irq_handler, 0,
>> +                   dev_name(gpu->dev), gpu);
>> +    if (err) {
>> +        dev_err(dev, "failed to request IRQ%u: %d\n", gpu->irq, err);
>> +        return err;
>> +    }
> 
> Shouldn't you disable the clk after devm_request_irq is called?

That's what I first thought, too. But then I found out, that merely 
enabling the clocks will clear the sparse interrupt and cause the 
handler not to be called during probe anymore.