linux-kernel - Re: [PATCH 1/7] irqchip/gic-v3: Add a DMA Non-Coherent flag

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Date:   Fri, 10 Mar 2023 07:04:16 -0500
From:   Peter Geis <pgwipeout@...il.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Lucas Tanure <lucas.tanure@...labora.com>,
        Vinod Koul <vkoul@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczynski <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>, Qu Wenruo <wqu@...e.com>,
        Piotr Oniszczuk <piotr.oniszczuk@...il.com>,
        Kever Yang <kever.yang@...k-chips.com>,
        linux-phy@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, kernel@...labora.com,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH 1/7] irqchip/gic-v3: Add a DMA Non-Coherent flag

On Fri, Mar 10, 2023 at 6:57 AM Marc Zyngier <maz@...nel.org> wrote:
>
> On Fri, 10 Mar 2023 11:41:46 +0000,
> Peter Geis <pgwipeout@...il.com> wrote:
> >
> > On Fri, Mar 10, 2023 at 3:05 AM Lucas Tanure <lucas.tanure@...labora.com> wrote:
> > >
> > > The GIC600 integration in RK356x, used in rk3588, doesn't support
> > > any of the shareability or cacheability attributes, and requires
> > > both values to be set to 0b00 for all the ITS and Redistributor
> > > tables.
> > >
> > > This is loosely based on prior work from XiaoDong Huang and
> > > Peter Geis fixing this issue specifically for Rockchip 356x.
> >
> > Good Morning,
> >
> > Since the gic is using dma, would it be reasonable to have all memory
> > allocations be requested with the GFP_DMA flag? Otherwise this doesn't
> > fully solve the problem for rk356x, where only the lower 4GB range is
> > DMA capable, but this tends to get allocated in the upper 4GB on 8GB
> > boards.
>
> That's an erratum. Please treat as such.

Good Morning,

Yes, believe me I'm fully aware of how broken rk356x is. I'm asking an
educational question from a kernel standards point of view, absent the
rk356x issues. Would it be reasonable that since the gic uses dma
memory, allocations for the gic should be made with the GFP_DMA flag?
Or is that a misuse of the flag?

Very Respectfully,
Peter Geis

>
>         M.
>
> --
> Without deviation from the norm, progress is not possible.