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From:   Alexander Stein <alexander.stein@ew.tq-group.com>
To:     Robin Murphy <robin.murphy@arm.com>, Frank Li <Frank.li@nxp.com>
Cc:     Lucas Stach <l.stach@pengutronix.de>, suzuki.poulose@arm.com,
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        Conor Dooley <conor+dt@kernel.org>,
        Shawn Guo <shawnguo@kernel.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Pengutronix Kernel Team <kernel@pengutronix.de>,
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Subject: Re: [PATCH 1/1] arm64: dts: imx8mp: remove arm, primecell-periphid at etm nodes
Date:   Fri, 07 Jul 2023 07:34:23 +0200
Message-ID: <24260662.6Emhk5qWAg@steina-w>
Organization: TQ-Systems GmbH
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References: <20230705205954.4159781-1-Frank.Li@nxp.com> <49ef52b7-0269-898c-7cc2-096f2f1037fc@arm.com> <ZKbSC8LBjLuo3ygD@lizhi-Precision-Tower-5810>
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Hi Frank,

Am Donnerstag, 6. Juli 2023, 16:39:07 CEST schrieb Frank Li:
> On Thu, Jul 06, 2023 at 12:06:19PM +0100, Robin Murphy wrote:
> > > > Am Mittwoch, 5. Juli 2023, 22:59:53 CEST schrieb Frank Li:
> > > > > The reg size of etm nodes is incorrectly set to 64k instead of 4k.
> > > > > This
> > > > > leads to a crash when calling amba_read_periphid().  After correc=
ted
> > > > > reg
> > > > > size, amba_read_periphid() retrieve the correct periphid.
> > > > > arm,primecell-periphid were removed from the etm nodes.
> > > >=20
> > > > So this means the reference manual is wrong here? It clearly states
> > > > the size is 64kiB. Reference Manual i.MX8MP Rev 1. 06/2021
> > > > On a side note: Is imx8mq affected by this as well? The DAP memory
> > > > table lists similar sizes in the RM .
> > >=20
> > > Note that the 64K MMIO space per device is really an alignment thing.
> > > It's a recommendation from ARM to allow individual device MMIO regions
> > > to be mapped on kernels with 64K page size. Most of the time the real
> > > MMIO space occupied by the device is actually much smaller than 64K.
> >=20
> > Indeed, it's quite common for TRM memory maps to be written in terms of
> > the
> > interconnect configuration, i.e. from the point of view of the
> > interconnect
> > itself, that whole range of address space is assigned to that periphera=
l,
> > and it may even be true that the entire range is routed to the port whe=
re
> > that peripheral is connected. However what's of more interest for DT is
> > how
> > much of that range the peripheral itself actually decodes.
>=20
> Yes, there are not problem by mapping bigger space in most case.
>=20
> amba bus's periphal use close to end of region to show device's identical
> information.

Ah, thanks for the explanation. This make things more clear.
But on the other is it sensible to assume the memory resource size to fit t=
he=20
IP address space? It appears to me the size is fixed to 4kiB anyway. Would =
it=20
make more sense to read the values from the address "base + 4K - x" instead=
 of=20
"base + size - x"?

Best regards,
Alexander

> In drivers/amba/bus.c,
>=20
> amba_read_periphid()
> {
> 	...
> 	size =3D resource_size(&dev->res);
> 	...
> 	for (pid =3D 0, i =3D 0; i < 4; i++)
> 		pid |=3D (readl(tmp + size - 0x20 + 4 * i) & 255) << (i *=20
8);
> }
>=20
> So the range in DTS for arm,primecell should be actual IP address space.
>=20
> > Robin.
> >=20
> > > _______________________________________________
> > > linux-arm-kernel mailing list
> > > linux-arm-kernel@lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel


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