linux-kernel - Re: [PATCH 1/5] iio: addac: ad74413r: add spi_device

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Date:   Mon, 14 Nov 2022 09:02:44 +0100
From:   Rasmus Villemoes <linux@...musvillemoes.dk>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Cosmin Tanislav <cosmin.tanislav@...log.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        devicetree@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Oleksij Rempel <linux@...pel-privat.de>
Subject: Re: [PATCH 1/5] iio: addac: ad74413r: add spi_device_id table

On 12/11/2022 17.50, Jonathan Cameron wrote:
> On Fri, 11 Nov 2022 15:39:17 +0100
> Rasmus Villemoes <linux@...musvillemoes.dk> wrote:
> 
>> Silence the run-time warning
>>
>>   SPI driver ad74413r has no spi_device_id for adi,ad74412r
>>
>> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
>> ---
>>  drivers/iio/addac/ad74413r.c | 8 ++++++++
>>  1 file changed, 8 insertions(+)
>>
>> diff --git a/drivers/iio/addac/ad74413r.c b/drivers/iio/addac/ad74413r.c
>> index 899bcd83f40b..37485be88a63 100644
>> --- a/drivers/iio/addac/ad74413r.c
>> +++ b/drivers/iio/addac/ad74413r.c
>> @@ -1457,12 +1457,20 @@ static const struct of_device_id ad74413r_dt_id[] = {
>>  };
>>  MODULE_DEVICE_TABLE(of, ad74413r_dt_id);
>>  
>> +static const struct spi_device_id ad74413r_spi_id[] = {
>> +	{ .name = "ad74412r", .driver_data = (kernel_ulong_t)&ad74412r_chip_info_data },
>> +	{ .name = "ad74413r", .driver_data = (kernel_ulong_t)&ad74413r_chip_info_data },
>> +	{},
> Trivial, but prefer not to have a comma after a "NULL" terminator like this.
> It would never make sense to add anything after it in the array.

I agree and wouldn't have added it if it weren't for the existing case
in the other table.

> Now you are matching existing driver style, but I'd still rather not see more
> instances of this added.

Sure.

> Also, driver_data is not currently used. It should be because adding this
> spi_id table means the driver can be probed via various routes where
> device_get_match_data() == NULL. 

That makes sense, I think I thought that that would somehow happen
automatically. Looking through the history of similar fixes, I see that
for example 3f8dd0a7dc does indeed add code as you suggest, but
855fe49984 does not (and also doesn't add the corresponding .driver_data
initializers in the spi table). They may very well both be correct, but
looping in Oleksij for good measure.

> Hence, alongside this change you need to have a fallback to cover that case.
> Something along the lines of...
> 
> 	st->chip_info = device_get_match_data(..);
> 	if (!st->chip_info) {
> 		struct spi_device_id *id = spi_get_device_id();
> 		if (!id)
> 			return -EINVAL;
> 
> 		st->chip_info = (void *)id->driver_data;
> 		//or better yet cast to the correct type I'm just too lazy to look it up ;)
> 		if (!st->chip_info)
> 			return -EINVAL;
> 
> 	}

Thanks,
Rasmus