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SubjectRe: [PATCH v4 1/4] can: dev: Add support for limiting configured bitrate
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Hello!

On 08/17/2017 08:54 PM, Franklin S Cooper Jr wrote:

>>> Various CAN or CAN-FD IP may be able to run at a faster rate than
>>> what the transceiver the CAN node is connected to. This can lead to
>>> unexpected errors. However, CAN transceivers typically have fixed
>>> limitations and provide no means to discover these limitations at
>>> runtime. Therefore, add support for a can-transceiver node that
>>> can be reused by other CAN peripheral drivers to determine for both
>>> CAN and CAN-FD what the max bitrate that can be used. If the user
>>> tries to configure CAN to pass these maximum bitrates it will throw
>>> an error.
>>>
>>> Signed-off-by: Franklin S Cooper Jr <fcooper@ti.com>
>>> ---
>>> Version 4 changes:
>>> Used can-transceiver instead of fixed-transceiver.
>>>
>>> drivers/net/can/dev.c | 50
>>> +++++++++++++++++++++++++++++++++++++++++++++++++
>>> include/linux/can/dev.h | 5 +++++
>>> 2 files changed, 55 insertions(+)
>>>
>>> diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
>>> index 365a8cc..372108f 100644
>>> --- a/drivers/net/can/dev.c
>>> +++ b/drivers/net/can/dev.c
>> [...]
>>> @@ -814,6 +815,39 @@ int open_candev(struct net_device *dev)
>>> }
>>> EXPORT_SYMBOL_GPL(open_candev);
>>> +#ifdef CONFIG_OF
>>> +/*
>>> + * Common function that can be used to understand the limitation of
>>> + * a transceiver when it provides no means to determine these
>>> limitations
>>> + * at runtime.
>>> + */
>>> +void of_can_transceiver(struct net_device *dev)
>>> +{
>>> + struct device_node *dn;
>>> + struct can_priv *priv = netdev_priv(dev);
>>> + struct device_node *np;
>>> + unsigned int max_bitrate;
>>> + int ret;
>>> +
>>> + np = dev->dev.parent->of_node;
>>
>> I'd do that as an initializer.
>
> Ok
>>
>>> +
>>> + dn = of_get_child_by_name(np, "can-transceiver");
>>> + if (!dn)
>>> + return;
>>> +
>>> + max_bitrate = 0;
>>> + ret = of_property_read_u32(dn, "max-bitrate", &max_bitrate);
>>
>> I'd initialize max_bitrate to 0 as iff of_property_read_u32() fails,
>> it'll leave the variable unset...>
>>> +
>>> + if (max_bitrate > 0) {
>>
>> You risk checking unset variable here.
>
> Four lines up I am already setting max_bitrate to a default value of 0.

Oops, sorry. Don't know how I missed that. Better done as initializer too
though...

MBR, Sergei

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