linux-kernel - Re: Re: [PATCH v6 2/5] HID: quirks: Refactor ELAN 400 and 401 handling

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Date:   Wed, 12 Jun 2019 16:20:42 -0600
From:   Jeffrey Hugo <jhugo@...eaurora.org>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Jeffrey Hugo <jeffrey.l.hugo@...il.com>
Cc:     benjamin.tissoires@...hat.com, jikos@...nel.org,
        hdegoede@...hat.com, bjorn.andersson@...aro.org, agross@...nel.org,
        lee.jones@...aro.org, xnox@...ntu.com, robh+dt@...nel.org,
        mark.rutland@....com, linux-input@...r.kernel.org,
        devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH v6 2/5] HID: quirks: Refactor ELAN 400 and 401
 handling

On 6/12/2019 3:46 PM, Dmitry Torokhov wrote:
> On Wed, Jun 12, 2019 at 02:27:21PM -0700, Jeffrey Hugo wrote:
>> There needs to be coordination between hid-quirks and the elan_i2c driver
>> about which devices are handled by what drivers.  Currently, both use
>> whitelists, which results in valid devices being unhandled by default,
>> when they should not be rejected by hid-quirks.  This is quickly becoming
>> an issue.
>>
>> Since elan_i2c has a maintained whitelist of what devices it will handle,
>> which is now in a header file that hid-quirks can access, use that to
>> implement a blacklist in hid-quirks so that only the devices that need to
>> be handled by elan_i2c get rejected by hid-quirks, and everything else is
>> handled by default.
>>
>> Suggested-by: Benjamin Tissoires <benjamin.tissoires@...hat.com>
>> Signed-off-by: Jeffrey Hugo <jeffrey.l.hugo@...il.com>
>> ---
>>   drivers/hid/hid-quirks.c | 27 ++++++++++++++++-----------
>>   1 file changed, 16 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/hid/hid-quirks.c b/drivers/hid/hid-quirks.c
>> index e5ca6fe2ca57..bd81bb090222 100644
>> --- a/drivers/hid/hid-quirks.c
>> +++ b/drivers/hid/hid-quirks.c
>> @@ -16,6 +16,7 @@
>>   #include <linux/export.h>
>>   #include <linux/slab.h>
>>   #include <linux/mutex.h>
>> +#include <linux/input/elan-i2c-ids.h>
>>   
>>   #include "hid-ids.h"
>>   
>> @@ -914,6 +915,8 @@ static const struct hid_device_id hid_mouse_ignore_list[] = {
>>   
>>   bool hid_ignore(struct hid_device *hdev)
>>   {
>> +	int i;
>> +
>>   	if (hdev->quirks & HID_QUIRK_NO_IGNORE)
>>   		return false;
>>   	if (hdev->quirks & HID_QUIRK_IGNORE)
>> @@ -978,18 +981,20 @@ bool hid_ignore(struct hid_device *hdev)
>>   		break;
>>   	case USB_VENDOR_ID_ELAN:
>>   		/*
>> -		 * Many Elan devices have a product id of 0x0401 and are handled
>> -		 * by the elan_i2c input driver. But the ACPI HID ELAN0800 dev
>> -		 * is not (and cannot be) handled by that driver ->
>> -		 * Ignore all 0x0401 devs except for the ELAN0800 dev.
>> +		 * Blacklist of everything that gets handled by the elan_i2c
>> +		 * input driver.  This avoids disabling valid touchpads and
>> +		 * other ELAN devices.
>>   		 */
>> -		if (hdev->product == 0x0401 &&
>> -		    strncmp(hdev->name, "ELAN0800", 8) != 0)
>> -			return true;
>> -		/* Same with product id 0x0400 */
>> -		if (hdev->product == 0x0400 &&
>> -		    strncmp(hdev->name, "QTEC0001", 8) != 0)
>> -			return true;
>> +		if ((hdev->product == 0x0401 || hdev->product == 0x0400)) {
>> +			for (i = 0; strlen(elan_acpi_id[i].id); ++i)
>> +				if (!strncmp(hdev->name, elan_acpi_id[i].id,
>> +					     strlen(elan_acpi_id[i].id)))
>> +					return true;
>> +			for (i = 0; strlen(elan_of_match[i].name); ++i)
>> +				if (!strncmp(hdev->name, elan_of_match[i].name,
>> +					     strlen(elan_of_match[i].name)))
>> +					return true;
> 
> Do we really need to blacklist the OF case here? I thought that in ACPI
> case we have clashes as HID gets matched by elan_i2c and CID is matched
> by i2c-hid, but I do not believe we'll run into the same situation on OF
> systems.

I think its the safer approach.

On an OF system, such as patch 3 in the series, the "hid-over-i2c" will 
end up running through this (kind of the whole reason why this series 
exists).  The vendor and product ids will still match, so we'll end up 
going through the lists to see if the hdev->name (the compatible string) 
will match the blacklist.  "hid-over-i2c" won't match the blacklist, but 
if there is a more specific compatible, it might.

In that case, not matching OF would work, however how it could break 
today is if both "hid-over-i2c" and "elan,ekth3000" were listed for the 
same device, and elan_i2c was not compiled.  In that case, if we skip 
the OF part of the black list, hid-quirks will not reject the device, 
and you'll probably have some odd behavior instead of the obvious "the 
device doesn't work because the correct driver isn't present" behavior.

While that scenario might be far fetched since having both 
"hid-over-i2c" and "elan,ekth3000" probably violates the OF bindings, 
its still safer to include the OF case in the blacklist against future 
scenarios.