Re: [PATCH 2/2 v16] drm/bridge: Add I2C based driver for ps8640 bridge

[Enric Balletbo Serra <eballetbo@gmail.com>]

2016-07-12 12:13 GMT+02:00 Daniel Vetter <daniel@ffwll.ch>:
> On Wed, Jun 29, 2016 at 6:31 AM, Daniel Kurtz <djkurtz@chromium.org> wrote:
>> On Fri, Jun 17, 2016 at 3:14 AM, Emil Velikov <emil.l.velikov@gmail.com> wrote:
>>>> +static ssize_t ps8640_update_fw_store(struct device *dev,
>>>> +                                     struct device_attribute *attr,
>>>> +                                     const char *buf, size_t count)
>>>> +{
>>>> +       struct i2c_client *client = to_i2c_client(dev);
>>>> +       struct ps8640 *ps_bridge = i2c_get_clientdata(client);
>>>> +       const struct firmware *fw;
>>>> +       int error;
>>>> +
>>>> +       error = request_firmware(&fw, PS_FW_NAME, dev);
>>> Can the device operate without a firmware ? If not, why is the
>>> firmware loaded so later/after user interaction (via sysfs) ? I don't
>>> recall any other driver in DRM to use such an approach.
>>
>> The PS8640 has internal flash, so it should always already have a
>> working firmware.
>> This sysfs interface is useful for user space initiated field firmware updates.
>
> Might be better to just do a request_firmware on driver load, and
> simply proceed if it's not there. Adding a sysfs interface (which is
> abi) seems way too much overkill for this imo. If you want to upgrade
> the firmware you can then just drop it into the right directory, with
> no further interaction needed.

IMHO I'm not sure if for this use case request_firmware on driver load
is a good idea. Flash the non-volatile internal chip can be a slow
operation and if you forget to remove the firmware after drop it into
the right directory apart from slow down the driver probe you can
damage the chip depending on the write endurance of the chip.

This sysfs interface is used on other subsystems when there is a
non-volatile memory, as example you can see at [1], [2]. Unfortunately
not all are using the same sysfs interface and maybe this should be
standardized (maybe it's an opportunity to define it)

Regards,
 Enric

[1] http://lxr.free-electrons.com/source/drivers/input/touchscreen/wdt87xx_i2c.c#L922
[2] http://lxr.free-electrons.com/source/drivers/scsi/pm8001/pm8001_ctl.c#L732


> -Daniel
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
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