From: Roman Kisel <romank@linux.microsoft.com>
To: Easwar Hariharan <eahariha@linux.microsoft.com>,
kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org,
decui@microsoft.com, linux-hyperv@vger.kernel.org,
rafael@kernel.org, lenb@kernel.org, linux-acpi@vger.kernel.org
Cc: ssengar@microsoft.com, sunilmut@microsoft.com
Subject: Re: [PATCH 1/6] arm64/hyperv: Support DeviceTree
Date: Mon, 20 May 2024 10:08:17 -0700 [thread overview]
Message-ID: <2c2ddc03-cf2e-4503-ba3b-7c221de666c2@linux.microsoft.com> (raw)
In-Reply-To: <e6f9761a-e542-417a-a2af-ba9f2bd253c4@linux.microsoft.com>
On 5/14/2024 5:00 PM, Easwar Hariharan wrote:
> On 5/14/2024 4:17 PM, Roman Kisel wrote:
>>
>>
>> On 5/14/2024 3:46 PM, Easwar Hariharan wrote:
>>> On 5/10/2024 10:42 AM, Roman Kisel wrote:
>>>>
>>>>
>>>> On 5/10/2024 10:04 AM, Easwar Hariharan wrote:
>>>>> On 5/10/2024 9:05 AM, romank@linux.microsoft.com wrote:
>>>>>> From: Roman Kisel <romank@linux.microsoft.com>
>>>>>>
>>>>>> Update the driver to support DeviceTree boot as well along with ACPI.
>>>>>> This enables the Virtual Trust Level platforms boot up on ARM64.
>>>>>>
>>>>>> Signed-off-by: Roman Kisel <romank@linux.microsoft.com>
>>>>>> ---
>>>>>> arch/arm64/hyperv/mshyperv.c | 34 +++++++++++++++++++++++++++++-----
>>>>>> 1 file changed, 29 insertions(+), 5 deletions(-)
>>>>>>
>>>>>> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c
>>>>>> index b1a4de4eee29..208a3bcb9686 100644
>>>>>> --- a/arch/arm64/hyperv/mshyperv.c
>>>>>> +++ b/arch/arm64/hyperv/mshyperv.c
>>>>>> @@ -15,6 +15,9 @@
>>>>>> #include <linux/errno.h>
>>>>>> #include <linux/version.h>
>>>>>> #include <linux/cpuhotplug.h>
>>>>>> +#include <linux/libfdt.h>
>>>>>> +#include <linux/of.h>
>>>>>> +#include <linux/of_fdt.h>
>>>>>> #include <asm/mshyperv.h>
>>>>>> static bool hyperv_initialized;
>>>>>> @@ -27,6 +30,29 @@ int hv_get_hypervisor_version(union hv_hypervisor_version_info *info)
>>>>>> return 0;
>>>>>> }
>>>>>> +static bool hyperv_detect_fdt(void)
>>>>>> +{
>>>>>> +#ifdef CONFIG_OF
>>>>>> + const unsigned long hyp_node = of_get_flat_dt_subnode_by_name(
>>>>>> + of_get_flat_dt_root(), "hypervisor");
>>>>>> +
>>>>>> + return (hyp_node != -FDT_ERR_NOTFOUND) &&
>>>>>> + of_flat_dt_is_compatible(hyp_node, "microsoft,hyperv");
>>>>>> +#else
>>>>>> + return false;
>>>>>> +#endif
>>>>>> +}
>>>>>> +
>>>>>> +static bool hyperv_detect_acpi(void)
>>>>>> +{
>>>>>> +#ifdef CONFIG_ACPI
>>>>>> + return !acpi_disabled &&
>>>>>> + !strncmp((char *)&acpi_gbl_FADT.hypervisor_id, "MsHyperV", 8);
>>>>>> +#else
>>>>>> + return false;
>>>>>> +#endif
>>>>>> +}
>>>>>> +
>>>>>
>>>>> Could using IS_ENABLED() allow collapsing these two functions into one hyperv_detect_fw()?
>>>>> I am wondering if #ifdef was explicitly chosen to allow for the code to be compiled in if CONFIG* is defined
>>>>> v/s IS_ENABLED() only being true if the CONFIG value is true.
>>>>>
>>>> In the hyperv_detect_fdt function, the #ifdef has been chosen due to the functions being declared only when the macro is defined, hence I could not rely on `if IS_ENABLED()` and the run-time detection. For the compile-time option, `#if IS_ENABLED()` would convey the intent better, could update with that.
>>>
>>> In patch 2/6, just under the diff you have, we already `select OF_EARLY_FLATTREE if OF`, so the declarations (and definitions)
>>> of the functions being present is already handled, AFAIK. Are we thinking there may be some weird config where neither OF nor
>>> ACPI is selected? If so, we should set a `depends on ACPI || OF` for config HYPERV to prevent that.
>>>
>>> I don't know if I'm missing something obvious here, so please correct me if I'm wrong.
>>>
>> I just sent out the v2 of the patch set, and (un?)fortunately missed the change I had for the #ifdef's in this chunk (to use #if IS_ENABLED() and remove pre-processor directives from the ACPI-related function).
>>
>> I am making the point that the change you are suggesting (as I understand) is this conditional statement
>>
>> if IS_ENABLED(CONFIG_OF) {
>> const unsigned long hyp_node = of_get_flat_dt_subnode_by_name(
>> of_get_flat_dt_root(), "hypervisor");
>>
>> return (hyp_node != -FDT_ERR_NOTFOUND) &&
>> of_flat_dt_is_compatible(hyp_node, "microsoft,hyperv");
>> }
>>
>
> That's right, that's the suggestion I'm making.
>
>> and for it to link successfully, one needs of_get_flat_dt_subnode_by_name defined. From the source code, that needs CONFIG_OF_EARLY_FLATTREE as there is no stub available when CONFIG_OF_EARLY_FLATTREE is not defined.
>
> We agree that you need of_get_flat_dt_subnode_by_name declared and defined, and it's not available, stub or otherwise, if CONFIG_OF_EARLY_FLATTREE is not defined.
>
> In my mind, I believed that either ACPI or OF had to be selected for some sort of firmware handoff to occur, but I did some experimentation and ended up with an
> x86_64 kernel config that has neither enabled, but nonetheless has CONFIG_HYPERV enabled. The kernel builds with such a config, whether it's useful for anything
> is another question. ARM64 requires CONFIG_OF so that side of the equation is clear.
>
> That's where my question above came in: Are we thinking there may be some weird config where neither OF nor ACPI is selected? I thought that was not a reasonable
> config, thus my prescription to set `depends on ACPI || OF` for config HYPERV. If there is a use case for an x86_64 kernel that has neither ACPI nor OpenFirmware/FDT,
> but nevertheless sets CONFIG_HYPERV, feel free to ignore this comment thread entirely.
>
Thanks for laying out the details so patiently for me! I believe I
understand your concerns better now. In the V2 of the patch series,
Michael Kelly suggested rethinking how the Kconfig change is carried
out. Appears natural to try out what your suggesting alongside with the
Michael's suggestions.
As for your other point, I wouldn't think, too, the system could boot or
be useful without some coordinates of the environment passed via ACPI || DT.
>
> Thanks,
> Easwar
--
Thank you,
Roman
next prev parent reply other threads:[~2024-05-20 17:08 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-10 16:04 [PATCH 0/6] arm64/hyperv: Support Virtual Trust Level boot romank
2024-05-10 16:05 ` [PATCH 1/6] arm64/hyperv: Support DeviceTree romank
2024-05-10 17:04 ` Easwar Hariharan
2024-05-10 17:42 ` Roman Kisel
2024-05-14 22:46 ` Easwar Hariharan
2024-05-14 23:17 ` Roman Kisel
2024-05-15 0:00 ` Easwar Hariharan
2024-05-20 17:08 ` Roman Kisel [this message]
2024-05-10 16:05 ` [PATCH 2/6] drivers/hv: Enable VTL mode for arm64 romank
2024-05-12 2:54 ` kernel test robot
2024-05-15 7:43 ` Wei Liu
2024-05-20 17:00 ` Roman Kisel
2024-05-10 16:05 ` [PATCH 3/6] arm64/hyperv: Boot in a Virtual Trust Level romank
2024-05-10 16:05 ` [PATCH 4/6] drivers/hv: arch-neutral implementation of get_vtl() romank
2024-05-10 16:05 ` [PATCH 5/6] drivers/hv/vmbus: Get the irq number from DeviceTree romank
2024-05-10 16:05 ` [PATCH 6/6] drivers/pci/hyperv/arm64: vPCI MSI IRQ domain from DT romank
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=2c2ddc03-cf2e-4503-ba3b-7c221de666c2@linux.microsoft.com \
--to=romank@linux.microsoft.com \
--cc=decui@microsoft.com \
--cc=eahariha@linux.microsoft.com \
--cc=haiyangz@microsoft.com \
--cc=kys@microsoft.com \
--cc=lenb@kernel.org \
--cc=linux-acpi@vger.kernel.org \
--cc=linux-hyperv@vger.kernel.org \
--cc=rafael@kernel.org \
--cc=ssengar@microsoft.com \
--cc=sunilmut@microsoft.com \
--cc=wei.liu@kernel.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 read-only IMAP folder(s) and NNTP newsgroup(s).