Re: [PATCH] hid: add force feedback support for SmartJoy PLUS PS2/USB adapter

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Quoting "Jiri Slaby" <jslaby@xxxxxxx>:

On 05/11/2009 05:17 PM, Jiri Kosina wrote:
On Fri, 8 May 2009, Jussi Kivilinna wrote:

This driver adds force feedback support for SmartJoy PLUS PS2/USB
adapter. I made this driver one device spesific instead of making
generic 'wisegroup-ff' because I have another Wisegroup PS2/USB adapter
that doesn't work same way as SmartJoy PLUS. If another device that is
compatible pops up, this driver could be then renamed to something more
generic.

Thanks for writing the driver!

--- a/drivers/hid/hid-core.c
+++ b/drivers/hid/hid-core.c
@@ -1312,6 +1312,9 @@ static const struct hid_device_id hid_blacklist[] = {
 	{ HID_USB_DEVICE(USB_VENDOR_ID_THRUSTMASTER, 0xb651) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_THRUSTMASTER, 0xb654) },
{ HID_USB_DEVICE(USB_VENDOR_ID_TOPSEED, USB_DEVICE_ID_TOPSEED_CYBERLINK) }, +#if defined(CONFIG_SMARTJOYPLUS_FF) || defined(CONFIG_SMARTJOYPLUS_FF_MODULE)
+	{ HID_USB_DEVICE(USB_VENDOR_ID_WISEGROUP, USB_DEVICE_ID_SMARTJOY_PLUS) },
+#endif
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ZEROPLUS, 0x0005) },
 	{ HID_USB_DEVICE(USB_VENDOR_ID_ZEROPLUS, 0x0030) },

Hmm, this isn't really compatible with what we have for other drivers, we
require the config option to be turned on in order to have support (i.e.
we include them into hid_blacklist unconditionally).

Strictly speaking, it depends on whether the device is able to be
managed by the generic layer or not. And it seems it can; this driver
adds only a FF support. If we disabled the FF support in the config and
the #if macro wasn't there, we would lose the device completely even
though it can be handled by the core, without FF though.


Yes, it works with generic layer. This problem exists with some other FF drivers as well, devices would work without FF support.

So I think, in this particular case, it is OK to have the conditional
line in there.

Or maybe better, to not taint the core code by such a bloat, leave
conditonal only the part of the driver which takes care of FF. The rest
of the driver (only the init/deinit) would be left as unable-to-disable
if !EMBEDDED, like other drivers.

I mean, two Kconfig entries, driver and FF support, driver is built
always if !EMBEDDED, FF is optional and dependent on the driver.
CONFIG_SMARTJOYPLUS_FF is then around sjoyff_init and *_play.


Ok, the same way as hid-pl.c?

I think hid-gaff.c/drff.c/tmff.c should do this as well.



Here comes some of my comments to the rest:

+#define debug(format, arg...) pr_debug("hid-sjoyff: " format "\n" , ## arg)

Define pr_fmt instead of this.

+static int hid_sjoyff_play(struct input_dev *dev, void *data,
+			 struct ff_effect *effect)
+{
+	struct hid_device *hid = input_get_drvdata(dev);
+	struct sjoyff_device *sjoyff = data;
+	u32 left, right;
+
+	left = effect->u.rumble.strong_magnitude;
+	right = effect->u.rumble.weak_magnitude;
+	debug("called with 0x%08x 0x%08x", left, right);
+
+	left = left * 0xff / 0xffff;

Confused here, * ff / ffff, what's the point? Is there any difference
with left /= 0xff?

It would actually be "left /= 0x101", and not as informative as "0xff / 0xffff".


Thanks for the driver.




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