On Wed, Jul 21, 2021 at 03:19:36AM +0000, Michael Kelley wrote:

From: Nathan Chancellor <nathan@kernel.org> Sent: Tuesday, July 20, 2021 6:56 PM

quoted

On Sun, Mar 21, 2021 at 08:53:40PM -0700, Dmitry Torokhov wrote:

quoted

Given that all serio drivers except one implement write() method
let's make it mandatory to avoid testing for its presence whenever
we attempt to use it.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
---
 drivers/input/serio/ams_delta_serio.c | 6 ++++++
 drivers/input/serio/serio.c           | 5 +++++
 include/linux/serio.h                 | 5 +----
 3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/input/serio/ams_delta_serio.c b/drivers/input/serio/ams_delta_serio.c
index 1c0be299f179..a1c314897951 100644
--- a/drivers/input/serio/ams_delta_serio.c
+++ b/drivers/input/serio/ams_delta_serio.c

@@ -89,6 +89,11 @@ static irqreturn_t ams_delta_serio_interrupt(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }

+static int ams_delta_serio_write(struct serio *serio, u8 data)
+{
+	return -EINVAL;
+}
+
 static int ams_delta_serio_open(struct serio *serio)
 {
 	struct ams_delta_serio *priv = serio->port_data;

@@ -157,6 +162,7 @@ static int ams_delta_serio_init(struct platform_device *pdev)
 	priv->serio = serio;

 	serio->id.type = SERIO_8042;
+	serio->write = ams_delta_serio_write;
 	serio->open = ams_delta_serio_open;
 	serio->close = ams_delta_serio_close;
 	strlcpy(serio->name, "AMS DELTA keyboard adapter", sizeof(serio->name));

diff --git a/drivers/input/serio/serio.c b/drivers/input/serio/serio.c
index 29f491082926..8d229a11bb6b 100644
--- a/drivers/input/serio/serio.c
+++ b/drivers/input/serio/serio.c

@@ -694,6 +694,11 @@ EXPORT_SYMBOL(serio_reconnect);
  */
 void __serio_register_port(struct serio *serio, struct module *owner)
 {
+	if (!serio->write) {
+		pr_err("%s: refusing to register %s without write method\n",
+		       __func__, serio->name);
+		return;
+	}
 	serio_init_port(serio);
 	serio_queue_event(serio, owner, SERIO_REGISTER_PORT);
 }

diff --git a/include/linux/serio.h b/include/linux/serio.h
index 6c27d413da92..075f1b8d76fa 100644
--- a/include/linux/serio.h
+++ b/include/linux/serio.h

@@ -121,10 +121,7 @@ void serio_unregister_driver(struct serio_driver *drv);

 static inline int serio_write(struct serio *serio, unsigned char data)
 {
-	if (serio->write)
-		return serio->write(serio, data);
-	else
-		return -1;
+	return serio->write(serio, data);
 }

 static inline void serio_drv_write_wakeup(struct serio *serio)
--

2.31.0.rc2.261.g7f71774620-goog


--
Dmitry

This patch as commit 81c7c0a350bf ("Input: serio - make write method
mandatory") in -next breaks input for my Hyper-V VM, which prevents me
from logging in. I attempted to do something like the following (-1 or
-EINVAL) which should be equivalent but it does not resolve the issue.

Cheers,
Nathan

diff --git a/drivers/input/serio/hyperv-keyboard.c b/drivers/input/serio/hyperv-keyboard.c
index 1a7b72a9016d..d3eee2d4c327 100644
--- a/drivers/input/serio/hyperv-keyboard.c
+++ b/drivers/input/serio/hyperv-keyboard.c

@@ -311,6 +311,11 @@ static void hv_kbd_stop(struct serio *serio)
        spin_unlock_irqrestore(&kbd_dev->lock, flags);
 }

+static int hv_kbd_write(struct serio *serio, u8 data)
+{
+       return -1;
+}
+
 static int hv_kbd_probe(struct hv_device *hv_dev,
                        const struct hv_vmbus_device_id *dev_id)
 {

@@ -341,6 +346,7 @@ static int hv_kbd_probe(struct hv_device *hv_dev,

        hv_serio->start = hv_kbd_start;
        hv_serio->stop = hv_kbd_stop;
+       hv_serio->write = hv_kbd_write;

        error = vmbus_open(hv_dev->channel,
                           KBD_VSC_SEND_RING_BUFFER_SIZE,

I'm seeing the same problem.  I've added the code to hyperv-keyboard.c that Nathan
proposed, and that solves the immediate problem in that the "refusing to register"
message no longer occurs.

But there's now a different problem in that this error is output whenever a key
is typed on the Hyper-V synthetic keyboard:

[   11.576716] atkbd serio0: keyboard reset failed on d34b2567-b9b6-42b9-8778-0a4ec0b

The Hyper-V keyboard driver depends on the AT Keyboard driver, and there's code in
atkbd.c that checks for the existence of the serio->write function.  I haven't debugged all
the details, but apparently hyperv-keyboard.c depends on atkbd.c finding that function
as NULL in order to work properly.   See atkbd_connect().  These messages are output
during boot when the two drivers are working properly together:

[    2.672693] hv_vmbus: registering driver hyperv_keyboard
[    2.700587] input: AT Translated Set 2 keyboard as /devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0004:00/VMBUS:00/d34b2567-b9b6-42b9-8778-0a4ec0b955bf/serio0/input/input1

I'm not seeing the second message when running the latest linux-next.

Yeah, the patch is busted as several drivers actually check for the
presence of serio->write() to adjust their behavior. I will revert the
patch.

Thanks!

-- 
Dmitry