linux-kernel - Re: [PATCH 06/11] RISC-V: drivers/iommu/riscv: Add command, fault, page-req queues

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Message-ID: <20230720-heftiness-refill-465b3d122049@spud>
Date:   Thu, 20 Jul 2023 19:43:01 +0100
From:   Conor Dooley <conor@...nel.org>
To:     Tomasz Jeznach <tjeznach@...osinc.com>
Cc:     Nick Kossifidis <mick@....forth.gr>,
        Anup Patel <apatel@...tanamicro.com>,
        Albert Ou <aou@...s.berkeley.edu>, linux@...osinc.com,
        Will Deacon <will@...nel.org>, Joerg Roedel <joro@...tes.org>,
        linux-kernel@...r.kernel.org, Sebastien Boeuf <seb@...osinc.com>,
        iommu@...ts.linux.dev, Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        linux-riscv@...ts.infradead.org,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 06/11] RISC-V: drivers/iommu/riscv: Add command, fault,
 page-req queues

On Thu, Jul 20, 2023 at 11:00:10AM -0700, Tomasz Jeznach wrote:
> On Wed, Jul 19, 2023 at 8:12 PM Nick Kossifidis <mick@....forth.gr> wrote:
> > On 7/19/23 22:33, Tomasz Jeznach wrote:
> > The description doesn't match the subject nor the patch content (we
> > don't jus enable interrupts, we also init the queues).
> >
> > > +     /* Parse Queue lengts */
> > > +     ret = of_property_read_u32(pdev->dev.of_node, "cmdq_len", &iommu->cmdq_len);
> > > +     if (!ret)
> > > +             dev_info(dev, "command queue length set to %i\n", iommu->cmdq_len);
> > > +
> > > +     ret = of_property_read_u32(pdev->dev.of_node, "fltq_len", &iommu->fltq_len);
> > > +     if (!ret)
> > > +             dev_info(dev, "fault/event queue length set to %i\n", iommu->fltq_len);
> > > +
> > > +     ret = of_property_read_u32(pdev->dev.of_node, "priq_len", &iommu->priq_len);
> > > +     if (!ret)
> > > +             dev_info(dev, "page request queue length set to %i\n", iommu->priq_len);
> > > +
> > >       dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
> > >
> >
> > We need to add those to the device tree binding doc (or throw them away,
> > I thought it would be better to have them as part of the device
> > desciption than a module parameter).

Aye, I didn't notice these. Any DT properties /must/ be documented.
To avoid having to make the comments on v2, properties should also not
contain underscores.

> We can add them as an optional fields to DT.
> Alternatively, I've been looking into an option to auto-scale CQ/PQ
> based on number of attached devices, but this gets trickier for
> hot-pluggable systems. I've added module parameters as a bare-minimum,
> but still looking for better solutions.

If they're properties of the hardware, they should come from DT/ACPI,
unless they're auto-detectable, in which case that is preferred.
To quote GregKH "please do not add new module parameters for drivers,
this is not the 1990s" :)

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