linux-kernel - Re: [Xen-devel] [PATCH 1/2] xen, input: add xen-kbdfront module parameter for setting resolution

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Date:   Mon, 10 Apr 2017 16:11:49 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Oleksandr Andrushchenko <andr2000@...il.com>,
        linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        linux-input@...r.kernel.org
Cc:     dmitry.torokhov@...il.com
Subject: Re: [Xen-devel] [PATCH 1/2] xen, input: add xen-kbdfront module
 parameter for setting resolution

On 10/04/17 16:00, Oleksandr Andrushchenko wrote:
> 
> 
> On 04/10/2017 04:50 PM, Juergen Gross wrote:
>> On 10/04/17 15:44, Oleksandr Andrushchenko wrote:
>>> Hi, Juergen!
>>>
>>> On 03/21/2017 07:19 PM, Juergen Gross wrote:
>>>> Add a parameter for setting the resolution of xen-kbdfront in order to
>>>> be able to cope with a (virtual) frame buffer of arbitrary resolution.
>>>>
>>>> Signed-off-by: Juergen Gross <jgross@...e.com>
>>>> ---
>>>>    drivers/input/misc/xen-kbdfront.c | 10 ++++++++--
>>>>    1 file changed, 8 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/input/misc/xen-kbdfront.c
>>>> b/drivers/input/misc/xen-kbdfront.c
>>>> index 3900875..2df5678 100644
>>>> --- a/drivers/input/misc/xen-kbdfront.c
>>>> +++ b/drivers/input/misc/xen-kbdfront.c
>>>> @@ -41,6 +41,12 @@ struct xenkbd_info {
>>>>        char phys[32];
>>>>    };
>>>>    +enum { KPARAM_WIDTH, KPARAM_HEIGHT, KPARAM_CNT };
>>>> +static int size[KPARAM_CNT] = { XENFB_WIDTH, XENFB_HEIGHT };
>>>> +module_param_array(size, int, NULL, 0444);
>>> is this by intention that you use 0444 here?
>>> It means read-only, thus one cannot change these,
>>> so what is the point of the module parameters then?
>> You can see the settings in sysfs.
> this is good so we can see actual width/height
> used by the pv driver
>> The values are settable via boot parameter.
> but then, if one has other values set in XenStore,
> these will/may be overridden, making it inconsistent,
> e.g. values loaded at start as module parameters
> (*size* array) is not going to be updated on
> XenbusStateInitWait/XenbusStateConnected. So, we'll
> end up with wrong parameters shown via sysfs
> one more question is why do we need module parameters
> if the same can be read from XenStore?

Because up to now nobody is setting the Xenstore values. This is
something I'm planning to do for Xen 4.10. Up to then we need a
workaround.

But you are right: The module parameters should be updated with
the values read from Xenstore.


Juergen