From: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
To: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>
Cc: Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>,
"linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org"
<linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org>,
iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org,
joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org,
"devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>
Subject: Re: [PATCH] drivers/of_iommu: ignore SMMU DT nodes with status 'disabled'
Date: Wed, 3 May 2017 11:58:30 +0100 [thread overview]
Message-ID: <4B3EA199-183C-40CE-8C7B-E55CD92FD402@linaro.org> (raw)
In-Reply-To: <1c0463e6-f82f-1179-4f54-b2d3de63dc87-5wv7dgnIgG8@public.gmane.org>
> On 3 May 2017, at 11:32, Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org> wrote:
>
>> On 28/04/17 14:22, Ard Biesheuvel wrote:
>>> On 28 April 2017 at 14:17, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org> wrote:
>>>> On Fri, Apr 28, 2017 at 02:14:49PM +0100, Ard Biesheuvel wrote:
>>>>> On 28 April 2017 at 14:11, Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org> wrote:
>>>>> Hi Ard,
>>>>>
>>>>> [+ devicetree@]
>>>>>
>>>>>> On Fri, Apr 14, 2017 at 01:43:15PM +0100, Ard Biesheuvel wrote:
>>>>>> DT nodes may have a status property, and if they do, such nodes should
>>>>>> only be considered present if the status property is set to 'okay'.
>>>>>>
>>>>>> Currently, we call the init function of IOMMUs described by the device
>>>>>> tree without taking this into account, which may result in the output
>>>>>> below on systems where some SMMUs may be legally disabled.
>>>>>>
>>>>>> Failed to initialise IOMMU /smb/smmu@e0200000
>>>>>> Failed to initialise IOMMU /smb/smmu@e0c00000
>>>>>> arm-smmu e0a00000.smmu: probing hardware configuration...
>>>>>> arm-smmu e0a00000.smmu: SMMUv1 with:
>>>>>> arm-smmu e0a00000.smmu: stage 2 translation
>>>>>> arm-smmu e0a00000.smmu: coherent table walk
>>>>>> arm-smmu e0a00000.smmu: stream matching with 32 register groups, mask 0x7fff
>>>>>> arm-smmu e0a00000.smmu: 8 context banks (8 stage-2 only)
>>>>>> arm-smmu e0a00000.smmu: Supported page sizes: 0x60211000
>>>>>> arm-smmu e0a00000.smmu: Stage-2: 40-bit IPA -> 40-bit PA
>>>>>> Failed to initialise IOMMU /smb/smmu@e0600000
>>>>>> Failed to initialise IOMMU /smb/smmu@e0800000
>>>>>>
>>>>>> Since this is not an error condition, only call the init function if
>>>>>> the device is enabled, which also inhibits the spurious error messages.
>>>>>>
>>>>>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
>>>>>> ---
>>>>>> drivers/iommu/of_iommu.c | 2 +-
>>>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
>>>>>> index 2683e9fc0dcf..2dd1206e6c0d 100644
>>>>>> --- a/drivers/iommu/of_iommu.c
>>>>>> +++ b/drivers/iommu/of_iommu.c
>>>>>> @@ -183,7 +183,7 @@ static int __init of_iommu_init(void)
>>>>>> for_each_matching_node_and_match(np, matches, &match) {
>>>>>> const of_iommu_init_fn init_fn = match->data;
>>>>>>
>>>>>> - if (init_fn(np))
>>>>>> + if (of_device_is_available(np) && init_fn(np))
>>>>>> pr_err("Failed to initialise IOMMU %s\n",
>>>>>> of_node_full_name(np));
>>>>>> }
>>>>>
>>>>> Is there a definition of what status = "disabled" is supposed to mean for an
>>>>> IOMMU? For example, that could mean that the firmware has pre-programmed the
>>>>> SMMU with particular translations or memory attributes (a bit like the
>>>>> CCA=1, CPM=1, DACS=0 case in ACPI IORT), or even disabled DMA traffic
>>>>> altogether.
>>>>>
>>>>> So I think we'd need an update to the generic IOMMU binding text to say
>>>>> exactly what the semantics are supposed to be here.
>>>>>
>>>>
>>>> I agree that it might make sense to describe the behavior of the IOMMU
>>>> when it is left in the state we found it in. But that is not the same
>>>> as status=disabled.
>>>>
>>>> The DTS subtree contains loads and loads of boilerplate
>>>> configurations, where only some pieces are enabled in the final image
>>>> by setting status=okay. So a node that has status 'disabled' should be
>>>> treated as 'not present', not as 'present but can be ignored under
>>>> assumptions such and such'
>>>>
>>>> In other words, I think we are talking about two different issues here.
>>>
>>> I'm not so sure... if we have a master device that has an iommus= property
>>> pointing to an IOMMU with status="disabled", I really don't know whether we
>>> should:
>>>
>>> 1. Assume the master can do DMA with a 1:1 mapping of memory and no
>>> changes to memory attributes
>>>
>>> 2. Assume the master can do DMA with a 1:1 mapping of memory, but
>>> potentially with changes to the attributes
>>>
>>> 3. Assume the master can do DMA, but with some pre-existing translation
>>> (what?)
>>>
>>> 4. Assume the master can't do DMA
>>>
>>> and I also don't know whether the "dma-coherent" property remains valid.
>>>
>>
>> Ah yes. Good point.
>>
>> So indeed, there should be some IOMMU specific status property that
>> can convey all of the above, or 1. and 4. at the minimum
>
> FWIW, the underlying issue being addressed here should be going away now
> anyway, since the now-queued probe deferral series obviates the init_fn
> early-device-creation bodge. I've been deliberately ignoring it for some
> time for precisely that reason ;)
>
Ok. I have also updated the Seattle firmware to remove the smmu nodes and the associated iommus/iommu-map properties entirely when disabling SMMU support in the firmware, which should address Will's concern regarding unspecified behavior of a disabled SMMU.
IOW, this patch can be disregarded. Thanks.
--
To unsubscribe from this list: send the line "unsubscribe devicetree" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
prev parent reply other threads:[~2017-05-03 10:58 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20170414124315.2401-1-ard.biesheuvel@linaro.org>
[not found] ` <20170414124315.2401-1-ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
2017-04-28 13:11 ` [PATCH] drivers/of_iommu: ignore SMMU DT nodes with status 'disabled' Will Deacon
[not found] ` <20170428131133.GJ13675-5wv7dgnIgG8@public.gmane.org>
2017-04-28 13:14 ` Ard Biesheuvel
[not found] ` <CAKv+Gu_G9fw0kwSetXmGjomc8Y_nu95O=rEVzgfafNRs0dtgvg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-04-28 13:17 ` Will Deacon
[not found] ` <20170428131744.GL13675-5wv7dgnIgG8@public.gmane.org>
2017-04-28 13:22 ` Ard Biesheuvel
[not found] ` <CAKv+Gu8L1iyzBitt8zzvWDDEXk_ysGfPRxHJbQQK5o8NMWF5MA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-05-03 10:32 ` Robin Murphy
[not found] ` <1c0463e6-f82f-1179-4f54-b2d3de63dc87-5wv7dgnIgG8@public.gmane.org>
2017-05-03 10:58 ` Ard Biesheuvel [this message]
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=4B3EA199-183C-40CE-8C7B-E55CD92FD402@linaro.org \
--to=ard.biesheuvel-qsej5fyqhm4dnm+yrofe0a@public.gmane.org \
--cc=devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org \
--cc=iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org \
--cc=joro-zLv9SwRftAIdnm+yROfE0A@public.gmane.org \
--cc=linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org \
--cc=mark.rutland-5wv7dgnIgG8@public.gmane.org \
--cc=robin.murphy-5wv7dgnIgG8@public.gmane.org \
--cc=will.deacon-5wv7dgnIgG8@public.gmane.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).