linux-kernel - Re: [PATCH 05/11] RISC-V: drivers/iommu/riscv: Add sysfs interface

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Date:   Thu, 20 Jul 2023 20:49:47 -0700
From:   Tomasz Jeznach <tjeznach@...osinc.com>
To:     Conor Dooley <conor@...nel.org>
Cc:     Krzysztof Kozlowski <krzk@...nel.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Anup Patel <apatel@...tanamicro.com>,
        Sunil V L <sunilvl@...tanamicro.com>,
        Nick Kossifidis <mick@....forth.gr>,
        Sebastien Boeuf <seb@...osinc.com>, iommu@...ts.linux.dev,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux@...osinc.com
Subject: Re: [PATCH 05/11] RISC-V: drivers/iommu/riscv: Add sysfs interface

On Thu, Jul 20, 2023 at 3:08 PM Conor Dooley <conor@...nel.org> wrote:
>
> On Thu, Jul 20, 2023 at 11:37:50PM +0200, Krzysztof Kozlowski wrote:
> > On 20/07/2023 20:30, Tomasz Jeznach wrote:
>
> > >>> +#define sysfs_dev_to_iommu(dev) \
> > >>> +     container_of(dev_get_drvdata(dev), struct riscv_iommu_device, iommu)
> > >>> +
> > >>> +static ssize_t address_show(struct device *dev,
> > >>> +                         struct device_attribute *attr, char *buf)
> > >>
> > >>
> > >> Where is the sysfs ABI documented?
> > >>
> > >
> > > Sysfs for now is used only to expose selected IOMMU memory mapped
> > > registers, with complete documentation in the RISC-V IOMMU Arch Spec
> > > [1], and some comments in iommu-bits.h file.
> > > LMK If it would be better to put a dedicated file documenting those
> > > with the patch itself.
> >
> > I meant, you created new sysfs interface. Maybe I missed something in
> > the patchset, but each new sysfs interface required documenting in
> > Documentation/ABI/.
>
> | expose selected IOMMU memory mapped registers
>
> | Enable sysfs debug / visibility interface providing restricted
> | access to hardware registers.
>
> Documentation requirements of sysfs stuff aside, I'm not sure that we
> even want a sysfs interface for this in the first place? Seems like, if
> at all, this should be debugfs instead? Seems like the only use case for
> it is debugging/development...

Thanks Conor, will switch to debugfs. This will be a more suitable interface.

regards,
- Tomasz