Re: [PATCH] HID: i2c-hid: add ACPI support

From: Benjamin Tissoires
Date: Tue Jan 08 2013 - 08:51:40 EST

Hi Mika,

On Tue, Jan 8, 2013 at 2:05 PM, Mika Westerberg
<mika.westerberg@xxxxxxxxxxxxxxx> wrote:
> The HID over I2C protocol specification states that when the device is
> enumerated from ACPI the HID descriptor address can be obtained by
> executing "_DSM" for the device with function 1. Enable this.

Hehe, funny thing, I worked on the very same patch last Friday. I was
not able to send it upstream as I still don't have an ACPI 5 enabled
device...
So thanks for submitting (and testing) this!

Before the review, I just have a quick question. All the HID/i2c
devices I saw so far present a reset line (through a GPIO). Does the
shipped device you have present this line, and if yes, how this meld
with the code (i.e. should we take this into account).

Please note that I can only compare this to my patch, based on the
DSDT example Microsoft gave in its spec. So sorry if I'm asking
useless things, but I like to understand... :)
Here are a few comments:

>
> Signed-off-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> ---
> drivers/hid/i2c-hid/i2c-hid.c | 73 +++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 71 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/hid/i2c-hid/i2c-hid.c b/drivers/hid/i2c-hid/i2c-hid.c
> index 9ef22244..b2eebb6 100644
> --- a/drivers/hid/i2c-hid/i2c-hid.c
> +++ b/drivers/hid/i2c-hid/i2c-hid.c
> @@ -34,6 +34,7 @@
> #include <linux/kernel.h>
> #include <linux/hid.h>
> #include <linux/mutex.h>
> +#include <linux/acpi.h>
>
> #include <linux/i2c/i2c-hid.h>
>
> @@ -810,6 +811,70 @@ static int __devinit i2c_hid_fetch_hid_descriptor(struct i2c_hid *ihid)
> return 0;
> }
>
> +#ifdef CONFIG_ACPI
> +static struct i2c_hid_platform_data *
> +i2c_hid_acpi_pdata(struct i2c_client *client)
> +{
> + static u8 i2c_hid_guid[] = {
> + 0xF7, 0xF6, 0xDF, 0x3C, 0x67, 0x42, 0x55, 0x45,
> + 0xAD, 0x05, 0xB3, 0x0A, 0x3D, 0x89, 0x38, 0xDE,
> + };
> + struct acpi_buffer buf = { ACPI_ALLOCATE_BUFFER, NULL };
> + struct i2c_hid_platform_data *pdata = NULL;
> + union acpi_object params[4], *obj;
> + struct acpi_object_list input;
> + struct acpi_device *adev;
> + acpi_handle handle;
> +
> + handle = ACPI_HANDLE(&client->dev);
> + if (!handle || acpi_bus_get_device(handle, &adev))
> + return NULL;
> +
> + input.count = ARRAY_SIZE(params);
> + input.pointer = params;
> +
> + params[0].type = ACPI_TYPE_BUFFER;
> + params[0].buffer.length = sizeof(i2c_hid_guid);
> + params[0].buffer.pointer = i2c_hid_guid;
> + params[1].type = ACPI_TYPE_INTEGER;
> + params[1].integer.value = 1;

Can you confirm that any value here is ok (this is what I read from
the DSDT example Microsoft gave, Arg1 is not used).

> + params[2].type = ACPI_TYPE_INTEGER;
> + params[2].integer.value = 1; /* HID function */
> + params[3].type = ACPI_TYPE_INTEGER;
> + params[3].integer.value = 0;

Again, the DSDT example showed that no Arg3 was used... But again, I
never wrote ACPI driver, so I may be wrong.

> +
> + if (ACPI_FAILURE(acpi_evaluate_object(handle, "_DSM", &input, &buf)))
> + return NULL;

As you are returning NULL here, the error that will be raised is
-EINVAL. I think it should be -ENODEV in this case. I have no strong
opinion on this, but this can be achieved by returning the error from
the function, and the returned i2c_hid_platform_data as an argument.

Or maybe just an error message will be sufficient.

> +
> + obj = (union acpi_object *)buf.pointer;
> + if (obj->type != ACPI_TYPE_INTEGER)
> + goto fail;

Again, I would like to know what happened here in case of a failure.
So an error message would be good.

> +
> + pdata = devm_kzalloc(&client->dev, sizeof(*pdata), GFP_KERNEL);
> + if (!pdata)
> + goto fail;

idem (and returning -ENOMEM would be better IMHO).

> +
> + pdata->hid_descriptor_address = obj->integer.value;
> +
> +fail:
> + kfree(buf.pointer);
> + return pdata;
> +}
> +
> +static struct acpi_device_id i2c_hid_acpi_match[] = {
> + {"ACPI0C50", 0 },

I never saw this _CID/_HID. Just out of curiosity, is this a
standardized _CID or is it a _HID specific to a device?

> + {"PNP0C50", 0 },
> + { },
> +};
> +MODULE_DEVICE_TABLE(acpi, i2c_hid_acpi_match);
> +#else
> +static inline struct i2c_hid_platform_data *
> +i2c_hid_acpi_pdata(struct i2c_client *client)
> +{
> + return NULL;
> +}
> +#endif
> +
> static int __devinit i2c_hid_probe(struct i2c_client *client,
> const struct i2c_device_id *dev_id)
> {
> @@ -822,8 +887,11 @@ static int __devinit i2c_hid_probe(struct i2c_client *client,
> dbg_hid("HID probe called for i2c 0x%02x\n", client->addr);
>
> if (!platform_data) {
> - dev_err(&client->dev, "HID register address not provided\n");
> - return -EINVAL;
> + platform_data = i2c_hid_acpi_pdata(client);
> + if (!platform_data) {
> + dev_err(&client->dev, "HID register address not provided\n");

You may have a line with more than 80 characters here (it's difficult
to guess thanks to my gmail client converting tabs into spaces...
grrr)

> + return -EINVAL;

Always returning -EINVAL does not seem to be the exact error code if
i2c_hid_acpi_pdata fails.

> + }
> }
>
> if (!client->irq) {
> @@ -964,6 +1032,7 @@ static struct i2c_driver i2c_hid_driver = {
> .name = "i2c_hid",
> .owner = THIS_MODULE,
> .pm = &i2c_hid_pm,
> + .acpi_match_table = ACPI_PTR(i2c_hid_acpi_match),

This is something I was wondering when looking at your documentation.
If CONFIG_ACPI is not defined, then 'i2c_hid_acpi_match' does not exists.
Is there some magic within ACPI_PTR if CONFIG_ACPI is not defined, or
should we put the #ifdef around?

Anyway thanks for this job!

Cheers,
Benjamin

> },
>
> .probe = i2c_hid_probe,
> --
> 1.7.10.4
>
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