linux-kernel - Re: [PATCH 1/4] of/fdt: Update zone_dma

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Date:   Thu, 1 Oct 2020 15:02:05 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        devicetree@...r.kernel.org, Will Deacon <will@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-mm <linux-mm@...ck.org>,
        Linux IOMMU <iommu@...ts.linux-foundation.org>,
        "moderated list:BROADCOM BCM2835 ARM ARCHITECTURE" 
        <linux-rpi-kernel@...ts.infradead.org>,
        Robin Murphy <robin.murphy@....com>,
        Christoph Hellwig <hch@....de>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/4] of/fdt: Update zone_dma_bits when running in bcm2711

On Thu, Oct 1, 2020 at 12:31 PM Nicolas Saenz Julienne
<nsaenzjulienne@...e.de> wrote:
>
> On Thu, 2020-10-01 at 18:23 +0100, Catalin Marinas wrote:
> > On Thu, Oct 01, 2020 at 06:15:01PM +0100, Catalin Marinas wrote:
> > > Hi Nicolas,
> > >
> > > Thanks for putting this together.
> > >
> > > On Thu, Oct 01, 2020 at 06:17:37PM +0200, Nicolas Saenz Julienne wrote:
> > > > diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> > > > index 4602e467ca8b..cd0d115ef329 100644
> > > > --- a/drivers/of/fdt.c
> > > > +++ b/drivers/of/fdt.c
> > > > @@ -25,6 +25,7 @@
> > > >  #include <linux/serial_core.h>
> > > >  #include <linux/sysfs.h>
> > > >  #include <linux/random.h>
> > > > +#include <linux/dma-direct.h>    /* for zone_dma_bits */
> > > >
> > > >  #include <asm/setup.h>  /* for COMMAND_LINE_SIZE */
> > > >  #include <asm/page.h>
> > > > @@ -1198,6 +1199,14 @@ void __init early_init_dt_scan_nodes(void)
> > > >   of_scan_flat_dt(early_init_dt_scan_memory, NULL);
> > > >  }
> > > >
> > > > +void __init early_init_dt_update_zone_dma_bits(void)
> > > > +{
> > > > + unsigned long dt_root = of_get_flat_dt_root();
> > > > +
> > > > + if (of_flat_dt_is_compatible(dt_root, "brcm,bcm2711"))
> > > > +         zone_dma_bits = 30;
> > > > +}
> > >
> > > I think we could keep this entirely in the arm64 setup_machine_fdt() and
> > > not pollute the core code with RPi4-specific code.
> >
> > Actually, even better, could we not move the check to
> > arm64_memblock_init() when we initialise zone_dma_bits?
>
> I did it this way as I vaguely remembered Rob saying he wanted to centralise
> all early boot fdt code in one place. But I'll be happy to move it there.

Right, unless zone_dma_bits is only an arm64 thing, then this doesn't
really have anything arch specific.

Reviewed-by: Rob Herring <robh@...nel.org>

Rob