Re: [PATCH 1/2] Increase HID_MAX_BUFFER_SIZE to 8KB to support additional, devices.

Re: [PATCH 1/2] Increase HID_MAX_BUFFER_SIZE to 8KB to support additional, devices.

[Jiri Kosina]

On Wed, 18 Nov 2020, Dean Camera wrote:

> Currently the maximum HID report size which can be buffered by the
> kernel is 8KB. This is sufficient for the vast majority of HID
> devices on the market, as most HID reports are fairly small.
> 
> However, some unusual devices such as the Elgate Stream Deck exist
> which use a report size slightly over 8KB for the image data that
> is sent to the device. Reports these large cannot be buffered by
> the regular HID subsystem currently, thus the only way to use such
> device is to bypass the HID subsystem entirely.
> 
> This increases the maximum HID report size to 16KB, which should
> cover all sanely designed HID devices.
> 
> Signed-off-by: Dean Camera <dean@fourwalledcubicle.com>

Dean,

thanks for the patch.

It has been whitespace-damaged by your mail client though. Could you 
please fix that and resubmit?

-- 
Jiri Kosina
SUSE Labs

Re: [PATCH 1/2] Increase HID_MAX_BUFFER_SIZE to 8KB to support additional, devices.

[Dean Camera]

Sure, I'll do that now (and do the same for my other unreviewed patch, 
which adds additional ioctls(). It's suprisingly frustratingly difficult 
to get Thunderbird to send a one-time unformatted plain-text email, as 
it seems to be a global setting that has to be changed.

I've given up on that and just set up git-send-email, which I've never 
used before but hope doesn't mangle anything.

Cheers!
- Dean

On 26/11/2020 12:12 am, Jiri Kosina wrote:
> On Wed, 18 Nov 2020, Dean Camera wrote:
> 
>> Currently the maximum HID report size which can be buffered by the
>> kernel is 8KB. This is sufficient for the vast majority of HID
>> devices on the market, as most HID reports are fairly small.
>>
>> However, some unusual devices such as the Elgate Stream Deck exist
>> which use a report size slightly over 8KB for the image data that
>> is sent to the device. Reports these large cannot be buffered by
>> the regular HID subsystem currently, thus the only way to use such
>> device is to bypass the HID subsystem entirely.
>>
>> This increases the maximum HID report size to 16KB, which should
>> cover all sanely designed HID devices.
>>
>> Signed-off-by: Dean Camera <dean@fourwalledcubicle.com>
> 
> Dean,
> 
> thanks for the patch.
> 
> It has been whitespace-damaged by your mail client though. Could you
> please fix that and resubmit?
> 

Re: [PATCH 1/2] Increase HID_MAX_BUFFER_SIZE to 8KB to support additional, devices.

[Dean Camera]

Argh, and of course I forgot I hadn't added the requisite cover letter 
and descriptions for those patches on that machine.

Sorry for the noise - I've sent V3 of both which should now be formatted 
correctly, and have the correct description.

- Dean

On 26/11/2020 9:26 am, Dean Camera wrote:
> Sure, I'll do that now (and do the same for my other unreviewed patch, 
> which adds additional ioctls(). It's suprisingly frustratingly difficult 
> to get Thunderbird to send a one-time unformatted plain-text email, as 
> it seems to be a global setting that has to be changed.
> 
> I've given up on that and just set up git-send-email, which I've never 
> used before but hope doesn't mangle anything.
> 
> Cheers!
> - Dean
> 
> On 26/11/2020 12:12 am, Jiri Kosina wrote:
>> On Wed, 18 Nov 2020, Dean Camera wrote:
>>
>>> Currently the maximum HID report size which can be buffered by the
>>> kernel is 8KB. This is sufficient for the vast majority of HID
>>> devices on the market, as most HID reports are fairly small.
>>>
>>> However, some unusual devices such as the Elgate Stream Deck exist
>>> which use a report size slightly over 8KB for the image data that
>>> is sent to the device. Reports these large cannot be buffered by
>>> the regular HID subsystem currently, thus the only way to use such
>>> device is to bypass the HID subsystem entirely.
>>>
>>> This increases the maximum HID report size to 16KB, which should
>>> cover all sanely designed HID devices.
>>>
>>> Signed-off-by: Dean Camera <dean@fourwalledcubicle.com>
>>
>> Dean,
>>
>> thanks for the patch.
>>
>> It has been whitespace-damaged by your mail client though. Could you
>> please fix that and resubmit?
>>

[PATCH 1/2] Increase HID_MAX_BUFFER_SIZE to 8KB to support additional, devices.

[Dean Camera]

Currently the maximum HID report size which can be buffered by the
kernel is 8KB. This is sufficient for the vast majority of HID
devices on the market, as most HID reports are fairly small.

However, some unusual devices such as the Elgate Stream Deck exist
which use a report size slightly over 8KB for the image data that
is sent to the device. Reports these large cannot be buffered by
the regular HID subsystem currently, thus the only way to use such
device is to bypass the HID subsystem entirely.

This increases the maximum HID report size to 16KB, which should
cover all sanely designed HID devices.

Signed-off-by: Dean Camera <dean@fourwalledcubicle.com>
---
  include/linux/hid.h | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/hid.h b/include/linux/hid.h
index 58684657960b..2faa7aba67ed 100644
--- a/include/linux/hid.h
+++ b/include/linux/hid.h
@@ -494,7 +494,7 @@ struct hid_report_enum {
  };

  #define HID_MIN_BUFFER_SIZE	64		/* make sure there is at least a 
packet size of space */
-#define HID_MAX_BUFFER_SIZE	8192		/* 8kb */
+#define HID_MAX_BUFFER_SIZE	16384		/* 16kb */
  #define HID_CONTROL_FIFO_SIZE	256		/* to init devices with >100 reports */
  #define HID_OUTPUT_FIFO_SIZE	64

-- 
2.25.1