linux-kernel - Re: [PATCH v2 2/2] mailbox: add STMicroelectronics STM32 IPCC driver

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Date:   Fri, 6 Apr 2018 12:29:02 +0000
From:   Fabien DESSENNE <fabien.dessenne@...com>
To:     Jassi Brar <jassisinghbrar@...il.com>
CC:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre TORGUE <alexandre.torgue@...com>,
        Ludovic BARRE <ludovic.barre@...com>,
        "Devicetree List" <devicetree@...r.kernel.org>,
        "\", linux-arm-kernel\"@lists.infradead.org" 
        <", linux-arm-kernel"@lists.infradead.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        srv_heupstream <linux-arm-kernel@...ts.infradead.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        Benjamin Gaignard <benjamin.gaignard@...aro.org>,
        Loic PALLARDY <loic.pallardy@...com>,
        "Arnaud POULIQUEN" <arnaud.pouliquen@...com>
Subject: Re: [PATCH v2 2/2] mailbox: add STMicroelectronics STM32 IPCC driver

Hi


On 05/04/18 11:38, Jassi Brar wrote:
> On Mon, Mar 12, 2018 at 4:28 PM, Fabien Dessenne <fabien.dessenne@...com> wrote:
> ....
>> +
>> +       /* irq */
>> +       for (i = 0; i < IPCC_IRQ_NUM; i++) {
>> +               ipcc->irqs[i] = of_irq_get_byname(dev->of_node, irq_name[i]);
>> +               if (ipcc->irqs[i] < 0) {
>> +                       dev_err(dev, "no IRQ specified %s\n", irq_name[i]);
>> +                       ret = ipcc->irqs[i];
>> +                       goto err_clk;
>> +               }
>> +
>> +               ret = devm_request_threaded_irq(dev, ipcc->irqs[i], NULL,
>> +                                               irq_thread[i], IRQF_ONESHOT,
>> +                                               dev_name(dev), ipcc);
>>
> In your interrupt handlers you don't do anything that could block.
> Threads only adds some delay to your message handling.
> So maybe use devm_request_irq() ?

The interrupt handlers call mbox_chan_received_data() / 
mbox_chan_txdone(), which call in turn client's rx_callback() / 
tx_done() / tx_prepare() which behavior may be unsafe. Hence, using a 
threaded irq here seems to be a good choice.


>
> .......
>> +
>> +static struct platform_driver stm32_ipcc_driver = {
>> +       .driver = {
>> +               .name = "stm32-ipcc",
>> +               .owner = THIS_MODULE,
>>
> No need of owner here these days.

OK, I will suppress it.

> And also maybe use readl/writel, instead of _relaxed.

The IPCC device is exclusively used on ARM. In ARM architecture, the 
ioremap on devices are strictly ordered and uncached.
In that case, using _relaxed avoids an unneeded cache flush, slightly 
improving performance.

>
> Cheers!