linux-kernel - Re: [PATCHv5 04/20] PCI: mobiveil: Remove the flag MSI_FLAG_MULTI_PCI

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Date:   Tue, 11 Jun 2019 18:29:49 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        "Z.q. Hou" <zhiqiang.hou@....com>
Cc:     "mark.rutland@....com" <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        Xiaowei Bao <xiaowei.bao@....com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "l.subrahmanya@...iveil.co.in" <l.subrahmanya@...iveil.co.in>,
        "will.deacon@....com" <will.deacon@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Leo Li <leoyang.li@....com>,
        "M.h. Lian" <minghuan.lian@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        Mingkai Hu <mingkai.hu@....com>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCHv5 04/20] PCI: mobiveil: Remove the flag
 MSI_FLAG_MULTI_PCI_MSI

On 11/06/2019 17:59, Lorenzo Pieralisi wrote:
> On Fri, Apr 12, 2019 at 08:35:36AM +0000, Z.q. Hou wrote:
>> From: Hou Zhiqiang <Zhiqiang.Hou@....com>
>>
>> The current code does not support multiple MSIs, so remove
>> the corresponding flag from the msi_domain_info structure.
> 
> Please explain me what's the problem before removing multi MSI
> support.

The reason seems to be the following code in the allocator:

        WARN_ON(nr_irqs != 1);
        mutex_lock(&msi->lock);

        bit = find_first_zero_bit(msi->msi_irq_in_use, msi->num_of_vectors);
        if (bit >= msi->num_of_vectors) {
                mutex_unlock(&msi->lock);
                return -ENOSPC;
        }

        set_bit(bit, msi->msi_irq_in_use);

So instead of fixing the allocator, the author prefers disabling
the feature. I'm not sure whether that is an acceptable outcome...

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...