linux-kernel - Re: [PATCH] irqchip/gic-v3-its: remove the shareability of ITS

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Date:   Wed, 07 Dec 2022 15:19:01 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     Harry Song <jundongsong1@...il.com>
Cc:     tglx@...utronix.de, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] irqchip/gic-v3-its: remove the shareability of ITS

On Wed, 07 Dec 2022 13:52:23 +0000,
Harry Song <jundongsong1@...il.com> wrote:
> 
> I know this is a very wrong patch, but my platform
> has an abnormal ITS problem caused by data consistency:
> My chip does not support Cache Coherent Interconnect (CCI).

That doesn't mean much. Nothing mandates to have a CCI, and plenty of
systems have other ways to maintain coherency.

> By default, ITS driver is the inner memory attribute.
> gits_write_cbaser() is used to write the inner memory
> attribute. But hw doesn't return the hardware's non-shareable
> property,so I don't think reading GITS_CBASER and GICR_PROPBASER
> here will get the real property of the current hardware: inner
> or outer shareable is not supported, so I would like to know
> whether ITS driver cannot be used on chips without CCI, or
> what method can be used to use ITS driver on chips without CCI?

It's not about CCI or not CCI. It is about which shareability domain
your ITS is in.

And it doesn't only affect the ITS. It also affects the
redistributors, and anything that accesses memory.

> 
> The current patch is designed to make ITS think that the current
> chip has no inner or outer memory properties, and then use
> its by flushing dcache.
> 
> This is the log for bug reports without patches:
> 
> [    0.000000] GICv3: CPU0: found redistributor 0 region 0:0x0000000003460000
> [    0.000000] ITS [mem 0x03440000-0x0345ffff]
> [    0.000000] ITS@...000000003440000: allocated 8192 Devices @41850000 (indirect, esz 8, psz 64K, shr 0)
> [    0.000000] ITS@...000000003440000: allocated 32768 Interrupt Collections @41860000 (flat, esz 2, psz 64K, shr 0)
> [    0.000000] GICv3: using LPI property table @0x0000000041870000
> [    0.000000] GICv3: CPU0: using allocated LPI pending table @0x0000000041880000
> [    0.000000] ITS queue timeout (64 1)
> [    0.000000] ITS cmd its_build_mapc_cmd failed
> [    0.000000] ITS queue timeout (128 1)
> [    0.000000] ITS cmd its_build_invall_cmd failed

Ah, this suspiciously looks like a Rockchip machine...

>
> Signed-off-by: Harry Song <jundongsong1@...il.com>
> ---
> 
> I am very sorry to bother you. This problem has been bothering me
> for several weeks.  I am looking forward to your reply.

If you have such issue, this needs to be handled as per-platform
quirk. I'm not putting such generic hacks in the driver.

	M.

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