linux-kernel - Re: [PATCH 1/4] can: dev: Add support for limiting configured bitrate

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Message-ID: <79d11682-83d8-f56b-4c17-8de1beec70f3@ti.com>
Date:   Thu, 20 Jul 2017 10:59:36 -0500
From:   Franklin S Cooper Jr <fcooper@...com>
To:     Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
        <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <netdev@...r.kernel.org>, <linux-can@...r.kernel.org>,
        <wg@...ndegger.com>, <mkl@...gutronix.de>, <robh+dt@...nel.org>,
        <quentin.schulz@...e-electrons.com>,
        <dev.kurt@...dijck-laurijssen.be>, <andrew@...n.ch>
Subject: Re: [PATCH 1/4] can: dev: Add support for limiting configured bitrate



On 07/20/2017 04:52 AM, Sergei Shtylyov wrote:
> Hello!
> 
> On 7/20/2017 2:36 AM, 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 fixed-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@...com>
>> ---
>>   drivers/net/can/dev.c   | 48
>> ++++++++++++++++++++++++++++++++++++++++++++++++
>>   include/linux/can/dev.h |  5 +++++
>>   2 files changed, 53 insertions(+)
>>
>> diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
>> index 365a8cc..fbab87d 100644
>> --- a/drivers/net/can/dev.c
>> +++ b/drivers/net/can/dev.c
> [...]
>> @@ -814,6 +830,38 @@ int open_candev(struct net_device *dev)
>>   }
>>   EXPORT_SYMBOL_GPL(open_candev);
>>   +#ifdef CONFIG_OF
>> +void of_transceiver_is_fixed(struct net_device *dev)
> 
>    Strange name for a *void* function...

Ok I see what you mean since I'm not actually returning anything. I'll
go with of_can_transceiver_fixed based on your comment also Oliver's
suggestion.

>    Also, I think 'struct net_device *' variables are typically called
> 'ndev'.

All other functions within this file uses struct net_device *dev. So I'm
just following the style currently used.

> 
>> +{
>> +    struct device_node *dn;
>> +    struct can_priv *priv = netdev_priv(dev);
>> +    u32 max_frequency;
>> +    struct device_node *np;
>> +
>> +    np = dev->dev.parent->of_node;
>> +
>> +    /* New binding */
>> +    dn = of_get_child_by_name(np, "fixed-transceiver");
>> +    if (!dn)
>> +        return;
>> +
>> +    of_property_read_u32(dn, "max-arbitration-speed", &max_frequency);
> 
>    In case this function fails, 'max_frequency' will have no value --
> you'd better initialize it...

Thanks for catching this. Will fix.

> 
>> +
>> +    if (max_frequency > 0)
>> +        priv->max_trans_arbitration_speed = max_frequency;
>> +    else
>> +        priv->max_trans_arbitration_speed = -1;
>> +
>> +    of_property_read_u32(dn, "max-data-speed", &max_frequency);
> 
>    Again, when that function fails, the variable will keep the value
> from the previous call...

Will fix.

> 
> [...]
> 
> MBR, Sergei