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

From: Jeffrey Hugo
Date: Wed Jun 19 2019 - 13:45:48 EST

On 6/19/2019 11:10 AM, Dmitry Torokhov wrote:
On Wed, Jun 12, 2019 at 04:20:42PM -0600, Jeffrey Hugo wrote:
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@xxxxxxxxxx>
Signed-off-by: Jeffrey Hugo <jeffrey.l.hugo@xxxxxxxxx>
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)
- * 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

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.

Yes, I believe it is quite far fetched. We are talking about someone
setting compatible sting to something that is decidedly not compatible.
I.e. we know that devices driven by elan_i2c are not compatible with
hi-over-i2c driver/protocol, so why do we expect that they both will be
specified in the same compatible string? I know ACPI case is messier in
this regard as 2 drivers look at the different data items when
evaluating whether they should bind to the device, but here we are
dealing with the same string.

Alright. Sounds like you really want the DT matching dropped, so I'll update the series with a new version ASAP that drops that.