linux-kernel - Re: [PATCH v2 6/9] PCI: dwc: Define maximum number of vectors

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Message-ID: <20180410095602.GA27363@e107981-ln.cambridge.arm.com>
Date:   Tue, 10 Apr 2018 10:56:02 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Gustavo Pimentel <gustavo.pimentel@...opsys.com>
Cc:     "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "Joao.Pinto@...opsys.com" <Joao.Pinto@...opsys.com>,
        "jingoohan1@...il.com" <jingoohan1@...il.com>,
        "kishon@...com" <kishon@...com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v2 6/9] PCI: dwc: Define maximum number of vectors

On Tue, Apr 10, 2018 at 08:59:30AM +0100, Gustavo Pimentel wrote:
> Hi Lorenzo,
> 
> On 09/04/2018 17:03, Lorenzo Pieralisi wrote:
> > On Mon, Apr 09, 2018 at 10:41:15AM +0100, Gustavo Pimentel wrote:
> >> Adds a callback that defines the maximum number of vectors that can be use
> >> by the Root Complex.
> >>
> >> Since this is a parameter associated to each SoC IP setting, makes sense to
> >> be configurable and easily visible to future modifications.
> >>
> >> The designware IP supports a maximum of 256 vectors.
> > 
> > I think that a DT property instead of a callback would have made more
> > sense - I struggle to see the point in defining a callback to initialize
> > a variable, this can be done in the generic dwc code (and a DT binding).
> 
> The addition of this callback was done in MSI-X patch series before I take over
> the PCIe Designware driver responsibility. However I remember a thread in which
> this subject was discussed (see [1]), maybe this could bring some light about
> the motive why is was done like this. If you don't agree I can do patch after
> this series only focusing on this topic in order to do like to suggested.
> 
> [1] -> https://www.spinics.net/lists/linux-pci/msg61835.html

Lucas has a point - it is fine to handle them as you do in this patch,
it does not make much sense to add a property for something that
strictly depends on the compatible string.

Thanks,
Lorenzo