Re: [PATCH 1/2] dell-wmi: Check if Dell WMI descriptor structure is valid

[Andy Lutomirski]

On Wed, Dec 30, 2015 at 3:27 AM, Michał Kępień  wrote:
>> > If you feel like I'm nit-picking and none of the above matters,
>> > please feel free to disregard my input and just follow your gut.
>>
>> It's ok. We just understand it quite differently. And in this case what
>> about changing commit message to something like this?
>>
>> ===
>> dell-wmi: Check if Dell WMI descriptor structure is valid
>>
>> After examining existing DSDT ACPI tables of more laptops and looking
>> into Dell WMI document mentioned in ML dicussion archived at
>> http://www.spinics.net/lists/platform-driver-x86/msg07220.html we will
>> parse and check WMI descriptor if contains expected data. It is because
>> WMI descriptor contains interface version number and it is needed to
>> know in next commit.
>> ===
>
> I like it way more than the previous one.
>

FWIW, the original version of this series works fine on my laptop
(after fixing the separate dmi_walk misuse bug).

--Andy
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Re: [PATCH 1/2] dell-wmi: Check if Dell WMI descriptor structure is valid

[Michał Kępień]

> > If you feel like I'm nit-picking and none of the above matters,
> > please feel free to disregard my input and just follow your gut.
> 
> It's ok. We just understand it quite differently. And in this case what 
> about changing commit message to something like this?
> 
> ===
> dell-wmi: Check if Dell WMI descriptor structure is valid
> 
> After examining existing DSDT ACPI tables of more laptops and looking 
> into Dell WMI document mentioned in ML dicussion archived at 
> http://www.spinics.net/lists/platform-driver-x86/msg07220.html we will 
> parse and check WMI descriptor if contains expected data. It is because 
> WMI descriptor contains interface version number and it is needed to 
> know in next commit.
> ===

I like it way more than the previous one.

-- 
Best regards,
Michał Kępień
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Re: [PATCH 1/2] dell-wmi: Check if Dell WMI descriptor structure is valid

[Pali Rohár]

On Tuesday 29 December 2015 13:44:13 Michał Kępień wrote:
> > > > According to Dell WMI document mentioned in ML dicussion
> > > > archived at
> > > > http://www.spinics.net/lists/platform-driver-x86/msg07220.html
> > > > OS should check Dell WMI descriptor structure.
> > > 
> > > "Should" or "can"?  I skimmed through the ACPI-WMI PDF and
> > > Mario's message again and I couldn't find any explicit statement
> > > urging the reader to check the structure in question before
> > > doing anything else.
> > 
> > That's questionable... In "Design flow" is first point that WMI
> > descriptor check.
> 
> Which "Design flow" are you referring to?  Because I found at least
> two: chapter 2.3 and a subsection of chapter 2.3.3.  Funnily enough,
> in both of these locations the WMI Descriptor Method is discussed
> first.
> 
> Personally, I wouldn't use the structure of that document to draw
> cause-effect conclusions.  Just look at the last chapter (2.3.4),
> which shows how to tell whether the BIOS supports the ACPI-WMI
> interface. Shouldn't that be the first thing to check, before doing
> anything else mentioned in that document?  Yet, it's the last thing
> discussed.
> 
> Anyway, while the document mentions in several places that the BIOS
> WMI Descriptor object can be queried, it fails to convince me as to
> why this is necessary at all as all values in the returned buffer
> are constant. Perhaps parsing the buffer is useful as a sanity check
> of some kind, but it certainly isn't a prerequisite for performing
> further actions.
> 
> Given the nature of your patchset, I'd personally rephrase the commit
> message(s) to state that according to your observations, there are
> behavioral differences between models with different versions of the
> WMI Interface, so we parse the WMI Descriptor object to determine
> which WMI Interface version is used on the machine we're running on.
>  Perhaps with an additional word or two that it won't hurt to also
> check the WMI Descriptor object's correctness while we're at it.
> 
> If you feel like I'm nit-picking and none of the above matters,
> please feel free to disregard my input and just follow your gut.

It's ok. We just understand it quite differently. And in this case what 
about changing commit message to something like this?

===
dell-wmi: Check if Dell WMI descriptor structure is valid

After examining existing DSDT ACPI tables of more laptops and looking 
into Dell WMI document mentioned in ML dicussion archived at 
http://www.spinics.net/lists/platform-driver-x86/msg07220.html we will 
parse and check WMI descriptor if contains expected data. It is because 
WMI descriptor contains interface version number and it is needed to 
know in next commit.
===

-- 
Pali Rohár
pali.ro...@gmail.com


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Re: [PATCH 1/2] dell-wmi: Check if Dell WMI descriptor structure is valid

[Michał Kępień]

> > > According to Dell WMI document mentioned in ML dicussion archived
> > > at http://www.spinics.net/lists/platform-driver-x86/msg07220.html
> > > OS should check Dell WMI descriptor structure.
> > 
> > "Should" or "can"?  I skimmed through the ACPI-WMI PDF and Mario's
> > message again and I couldn't find any explicit statement urging the
> > reader to check the structure in question before doing anything else.
> 
> That's questionable... In "Design flow" is first point that WMI 
> descriptor check.

Which "Design flow" are you referring to?  Because I found at least two:
chapter 2.3 and a subsection of chapter 2.3.3.  Funnily enough, in both
of these locations the WMI Descriptor Method is discussed first.

Personally, I wouldn't use the structure of that document to draw
cause-effect conclusions.  Just look at the last chapter (2.3.4), which
shows how to tell whether the BIOS supports the ACPI-WMI interface.
Shouldn't that be the first thing to check, before doing anything else
mentioned in that document?  Yet, it's the last thing discussed.

Anyway, while the document mentions in several places that the BIOS WMI
Descriptor object can be queried, it fails to convince me as to why this
is necessary at all as all values in the returned buffer are constant.
Perhaps parsing the buffer is useful as a sanity check of some kind, but
it certainly isn't a prerequisite for performing further actions.

Given the nature of your patchset, I'd personally rephrase the commit
message(s) to state that according to your observations, there are
behavioral differences between models with different versions of the WMI
Interface, so we parse the WMI Descriptor object to determine which WMI
Interface version is used on the machine we're running on.  Perhaps with
an additional word or two that it won't hurt to also check the WMI
Descriptor object's correctness while we're at it.

If you feel like I'm nit-picking and none of the above matters, please
feel free to disregard my input and just follow your gut.

-- 
Best regards,
Michał Kępień
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Re: [PATCH 1/2] dell-wmi: Check if Dell WMI descriptor structure is valid

[Michał Kępień]

> According to Dell WMI document mentioned in ML dicussion archived at
> http://www.spinics.net/lists/platform-driver-x86/msg07220.html OS should
> check Dell WMI descriptor structure.

"Should" or "can"?  I skimmed through the ACPI-WMI PDF and Mario's
message again and I couldn't find any explicit statement urging the
reader to check the structure in question before doing anything else.

-- 
Best regards,
Michał Kępień
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Re: [PATCH 1/2] dell-wmi: Check if Dell WMI descriptor structure is valid

[Pali Rohár]

On Monday 28 December 2015 14:37:07 Michał Kępień wrote:
> > According to Dell WMI document mentioned in ML dicussion archived
> > at http://www.spinics.net/lists/platform-driver-x86/msg07220.html
> > OS should check Dell WMI descriptor structure.
> 
> "Should" or "can"?  I skimmed through the ACPI-WMI PDF and Mario's
> message again and I couldn't find any explicit statement urging the
> reader to check the structure in question before doing anything else.

That's questionable... In "Design flow" is first point that WMI 
descriptor check.

-- 
Pali Rohár
pali.ro...@gmail.com


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Re: [PATCH 1/2] dell-wmi: Check if Dell WMI descriptor structure is valid

[Pali Rohár]

On Friday 25 December 2015 02:23:04 Andy Lutomirski wrote:
> On Thu, Dec 24, 2015 at 1:18 PM, Pali Rohár 
> wrote:
> > According to Dell WMI document mentioned in ML dicussion archived
> > at http://www.spinics.net/lists/platform-driver-x86/msg07220.html
> > OS should check Dell WMI descriptor structure. Structure also
> > provide Dell WMI interface version which is used later.
> 
> I will rebase my big series on top of this.  It'll give me a good
> excuse to test that I got the probe ordering right.  (The code is
> explicitly intended to support use cases like this, and now I'll have
> a real-world test for it.)  I'll also test this in a bit.

Ok!

> > +MODULE_ALIAS("wmi:"DELL_DESCRIPTOR_GUID);
> 
> I don't think this is necessary.  The driver will only work if both
> wmi devices and, hence, modaliases are present, so there's no need to
> cause just one or the other to trigger dell-wmi autoloading.

Maybe now when you are working on big WMI patch series is time to change 
modalias support in WMI to support AND-conjunction (&&) on WMI aliases, 
not just OR (one alias match).

Something like: load dell-wmi.ko driver if system provides both WMI 
GUIDs.

> > +/**
> 
> > + * Descriptor buffer is 128 byte long and contains:
> This isn't kerneldoc format, so I think this should just be "/*".
> 

Ok, I will fix this in next version.

> > +   if (obj->buffer.length != 128) {
> > +   pr_err("Dell descriptor buffer has invalid length
> > (%d)\n", +   obj->buffer.length);
> > +   kfree(obj);
> > +   return -EINVAL;
> > +   }
> 
> I would advocate for being more permissive: a buffer that is actually
> too short for the fields we need would result in -EINVAL, but a
> buffer that isn't 128 bytes would just be a warning and not cause
> module load to fail.
> 
> --Andy

Sounds good, I will change this part.

-- 
Pali Rohár
pali.ro...@gmail.com


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Re: [PATCH 1/2] dell-wmi: Check if Dell WMI descriptor structure is valid

[Andy Lutomirski]

On Thu, Dec 24, 2015 at 1:18 PM, Pali Rohár  wrote:
> According to Dell WMI document mentioned in ML dicussion archived at
> http://www.spinics.net/lists/platform-driver-x86/msg07220.html OS should
> check Dell WMI descriptor structure. Structure also provide Dell WMI
> interface version which is used later.

I will rebase my big series on top of this.  It'll give me a good
excuse to test that I got the probe ordering right.  (The code is
explicitly intended to support use cases like this, and now I'll have
a real-world test for it.)  I'll also test this in a bit.

> +MODULE_ALIAS("wmi:"DELL_DESCRIPTOR_GUID);

I don't think this is necessary.  The driver will only work if both
wmi devices and, hence, modaliases are present, so there's no need to
cause just one or the other to trigger dell-wmi autoloading.

> +/**
> + * Descriptor buffer is 128 byte long and contains:

This isn't kerneldoc format, so I think this should just be "/*".

> +   if (obj->buffer.length != 128) {
> +   pr_err("Dell descriptor buffer has invalid length (%d)\n",
> +   obj->buffer.length);
> +   kfree(obj);
> +   return -EINVAL;
> +   }

I would advocate for being more permissive: a buffer that is actually
too short for the fields we need would result in -EINVAL, but a buffer
that isn't 128 bytes would just be a warning and not cause module load
to fail.

--Andy
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[PATCH 1/2] dell-wmi: Check if Dell WMI descriptor structure is valid

[Pali Rohár]

According to Dell WMI document mentioned in ML dicussion archived at
http://www.spinics.net/lists/platform-driver-x86/msg07220.html OS should
check Dell WMI descriptor structure. Structure also provide Dell WMI
interface version which is used later.

Signed-off-by: Pali Rohár 
---
 drivers/platform/x86/dell-wmi.c |   78 ++-
 1 file changed, 76 insertions(+), 2 deletions(-)

diff --git a/drivers/platform/x86/dell-wmi.c b/drivers/platform/x86/dell-wmi.c
index 57402c4..09ee8ed 100644
--- a/drivers/platform/x86/dell-wmi.c
+++ b/drivers/platform/x86/dell-wmi.c
@@ -2,6 +2,7 @@
  * Dell WMI hotkeys
  *
  * Copyright (C) 2008 Red Hat 
+ * Copyright (C) 2014-2015 Pali Rohár 
  *
  * Portions based on wistron_btns.c:
  * Copyright (C) 2005 Miloslav Trmac 
@@ -38,14 +39,18 @@
 #include 
 
 MODULE_AUTHOR("Matthew Garrett ");
+MODULE_AUTHOR("Pali Rohár ");
 MODULE_DESCRIPTION("Dell laptop WMI hotkeys driver");
 MODULE_LICENSE("GPL");
 
 #define DELL_EVENT_GUID "9DBB5994-A997-11DA-B012-B622A1EF5492"
+#define DELL_DESCRIPTOR_GUID "8D9DDCBC-A997-11DA-B012-B622A1EF5492"
 
 static int acpi_video;
+static u32 dell_wmi_interface_version;
 
 MODULE_ALIAS("wmi:"DELL_EVENT_GUID);
+MODULE_ALIAS("wmi:"DELL_DESCRIPTOR_GUID);
 
 /*
  * Certain keys are flagged as KE_IGNORE. All of these are either
@@ -422,16 +427,85 @@ static void __init find_hk_type(const struct dmi_header 
*dm, void *dummy)
}
 }
 
+/**
+ * Descriptor buffer is 128 byte long and contains:
+ *
+ *   Name Offset  Length  Value
+ * Vendor Signature  0   4"DELL"
+ * Object Signature  4   4" WMI"
+ * WMI Interface Version 8   4
+ * WMI buffer length12   44096
+ */
+static int __init dell_wmi_check_descriptor_buffer(void)
+{
+   struct acpi_buffer out = { ACPI_ALLOCATE_BUFFER, NULL };
+   union acpi_object *obj;
+   acpi_status status;
+   u32 *buffer;
+
+   status = wmi_query_block(DELL_DESCRIPTOR_GUID, 0, );
+   if (ACPI_FAILURE(status)) {
+   pr_err("Cannot read Dell descriptor buffer - %d\n", status);
+   return status;
+   }
+
+   obj = (union acpi_object *)out.pointer;
+   if (!obj) {
+   pr_err("Dell descriptor buffer is empty\n");
+   return -EINVAL;
+   }
+
+   if (obj->type != ACPI_TYPE_BUFFER) {
+   pr_err("Cannot read Dell descriptor buffer\n");
+   kfree(obj);
+   return -EINVAL;
+   }
+
+   if (obj->buffer.length != 128) {
+   pr_err("Dell descriptor buffer has invalid length (%d)\n",
+   obj->buffer.length);
+   kfree(obj);
+   return -EINVAL;
+   }
+
+   buffer = (u32 *)obj->buffer.pointer;
+
+   if (buffer[0] != 0x4C4C4544 && buffer[1] != 0x494D5720)
+   pr_warn("Dell descriptor buffer has invalid signature (%*ph)\n",
+   8, buffer);
+
+   if (buffer[2] != 0 && buffer[2] != 1)
+   pr_warn("Dell descriptor buffer has unknown version (%d)\n",
+   buffer[2]);
+
+   if (buffer[3] != 4096)
+   pr_warn("Dell descriptor buffer has invalid buffer length 
(%d)\n",
+   buffer[3]);
+
+   dell_wmi_interface_version = buffer[2];
+
+   pr_info("Detected Dell WMI interface version %u\n",
+   dell_wmi_interface_version);
+
+   kfree(obj);
+   return 0;
+}
+
 static int __init dell_wmi_init(void)
 {
int err;
acpi_status status;
 
-   if (!wmi_has_guid(DELL_EVENT_GUID)) {
-   pr_warn("No known WMI GUID found\n");
+   if (!wmi_has_guid(DELL_EVENT_GUID) ||
+   !wmi_has_guid(DELL_DESCRIPTOR_GUID)) {
+   pr_warn("Dell WMI GUID were not found\n");
return -ENODEV;
}
 
+   err = dell_wmi_check_descriptor_buffer();
+   if (err)
+   return err;
+
dmi_walk(find_hk_type, NULL);
acpi_video = acpi_video_get_backlight_type() != acpi_backlight_vendor;
 
-- 
1.7.9.5

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