lkml.org 
[lkml]   [2014]   [Apr]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [RFC PATCH 0/2] managed token devres interfaces
On Wed, Apr 09, 2014 at 09:21:06AM -0600, Shuah Khan wrote:
> Media devices often have hardware resources that are shared
> across several functions. For instance, TV tuner cards often
> have MUXes, converters, radios, tuners, etc. that are shared
> across various functions. However, v4l2, alsa, DVB, usbfs, and
> all other drivers have no knowledge of what resources are
> shared. For example, users can't access DVB and alsa at the same
> time, or the DVB and V4L analog API at the same time, since many
> only have one converter that can be in either analog or digital
> mode. Accessing and/or changing mode of a converter while it is
> in use by another function results in video stream error.
>
> A shared devres that can be locked and unlocked by various drivers
> that control media functions on a single media device is needed to
> address the above problems.
>
> A token devres that can be looked up by a token for locking, try
> locking, unlocking will help avoid adding data structure
> dependencies between various media drivers. This token is a unique
> string that can be constructed from a common data structure such as
> struct device, bus_name, and hardware address.
>
> The devm_token_* interfaces manage access to token resource.
>
> Interfaces:
> devm_token_create()
> devm_token_destroy()
> devm_token_lock()
> devm_token_unlock()
> Usage:
> Create token:
> Call devm_token_create() with a token id which is a unique
> string.
> Lock token: Call devm_token_lock() to lock or try lock a token.
> Unlock token: Call devm_token_unlock().
> Destroy token: Call devm_token_destroy() to delete the token.
>
> A new devres_* interface to update the status of this token resource
> to busy when locked and free when unlocked is necessary to implement
> this new managed resource.
>
> devres_update() searches for the resource that matches supplied match
> criteria similar to devres_find(). When a match is found, it calls
> the update function caller passed in.
>
> This patch set adds a new devres_update) interface and token devres
> interfaces.
>
> Test Cases for token devres interfaces: (passed)
> - Create, lock, unlock, and destroy sequence.
> - Try lock while it is locked. Returns -EBUSY as expected.
> - Try lock after destroy. Returns -ENODEV as expected.
> - Unlock while it is unlocked. Returns 0 as expected. This is a no-op.
> - Try unlock after destroy. Returns -ENODEV as expected.

Any chance you can add these "test cases" as part of the kernel code so
it lives here for any future changes?

> Special notes for Mauro Chehab:
> - Please evaluate if these token devres interfaces cover all media driver
> use-cases. If not what is needed to cover them.
> - For use-case testing, I generated a string from em28xx device, as this
> is common for all em28xx extensions: (hope this holds true when em28xx
> uses snd-usb-audio
> - Construct string with (dev is struct em28xx *dev)
> format: "tuner:%s-%s-%d"
> with the following:
> dev_name(&dev->udev->dev)
> dev->udev->bus->bus_name
> dev->tuner_addr
> - I added test code to em28xx_card_setup() to test the interfaces:
> example token from this test code generated with the format above:

What would the driver changes look like to take advantage of these new
functions?

thanks,

greg k-h


\
 
 \ /
  Last update: 2014-04-09 22:01    [W:0.693 / U:0.048 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site