Subject: Re: [PATCH 2/2] can: sja1000: of: add compatibility with Technologic Systems version

From: Marc Kleine-Budde <[email-masked]>
Date: Fri, 18 Dec 2015 22:05:01 +0100

On 12/18/2015 10:02 PM, Damien Riegel wrote:
> On Fri, Dec 18, 2015 at 09:41:47PM +0100, Marc Kleine-Budde wrote:
>> On 12/18/2015 09:17 PM, Damien Riegel wrote:
>>> Technologic Systems provides an IP compatible with the SJA1000,
>>> instantiated in an FPGA. Because of some bus widths issue, access to
>>> registers is made through a "window" that works like this:
>>>
>>>     base + 0x0: address to read/write
>>>     base + 0x2: 8-bit register value
>>>
>>> This commit adds a new compatible device, "technologic,sja1000", with
>>> read and write functions using the window mechanism.
>>>
>>> Signed-off-by: Damien Riegel <[email-masked]>
>>> ---
>>>  drivers/net/can/sja1000/sja1000_platform.c | 30 ++++++++++++++++++++++++++++--
>>>  1 file changed, 28 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/net/can/sja1000/sja1000_platform.c b/drivers/net/can/sja1000/sja1000_platform.c
>>> index 0552ed4..6cbf251 100644
>>> --- a/drivers/net/can/sja1000/sja1000_platform.c
>>> +++ b/drivers/net/can/sja1000/sja1000_platform.c
>>> @@ -70,6 +70,18 @@ static void sp_write_reg32(const struct sja1000_priv *priv, int reg, u8 val)
>>>  	iowrite8(val, priv->reg_base + reg * 4);
>>>  }
>>>  
>>> +static u8 ts4800_read_reg16(const struct sja1000_priv *priv, int reg)
>>> +{
>>> +	sp_write_reg16(priv, 0,  reg);
>>> +	return sp_read_reg16(priv, 2);
>>
>> This is racy, please add a spinlock.
>>
>>> +}
>>> +
>>> +static void ts4800_write_reg16(const struct sja1000_priv *priv, int reg, u8 val)
>>> +{
>>> +	sp_write_reg16(priv, 0, reg);
>>> +	sp_write_reg16(priv, 2, val);
>>
>> This is racy, too.
>>
>> Have a look at https://marc.info/?l=linux-can&m=137149497403825&w=2
> 
> Thank you for the link. In my situation, I don't think there is a race
> issue at the bus level, so a per-device spinlock should be enough. Would
> that be an acceptable patch? It would look a lot like the patch you
> suggested in the thread you linked, just rebased on current version.

Yes, but for a device spinlock you probably have to remove "const" from
the priv pointer.

Marc

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