[PATCH linux dev-5.4] fsi: core: Set slave local bus ownership during init

[Eddie James]

On 6/1/20 9:05 PM, Joel Stanley wrote:
> On Wed, 20 May 2020 at 18:17, Eddie James <eajames at linux.ibm.com> wrote:
>> The driver ought to claim local bus ownership of the slave it's
>> communicating with.
> I am not familiar with this register's purpose so feel free to explain
> the details.


Sure, I'll add a comment. I don't really understand the details either, 
but I think this is effectively for multi-master setups. The slave (in 
theory) will deny access to masters who try to access the CFAM address 
space but who don't "own" the bus.

>
> Should we also "un-claim" ownership at any point?


Well, the driver doesn't seem to perform any other teardown, so I don't 
think so. Also I'm not aware of any multi-master setup using this driver 
so it shouldn't actually matter. Also, the hardware doesn't seem to 
enforce this despite being required in the specification...


Thanks,

Eddie


>
>> Signed-off-by: Eddie James <eajames at linux.ibm.com>
>> ---
>>   drivers/fsi/fsi-core.c | 16 +++++++++++++++-
>>   1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/fsi/fsi-core.c b/drivers/fsi/fsi-core.c
>> index 8244da8a7241..48424b672295 100644
>> --- a/drivers/fsi/fsi-core.c
>> +++ b/drivers/fsi/fsi-core.c
>> @@ -50,6 +50,7 @@ static const int engine_page_size = 0x400;
>>   #define FSI_SMODE              0x0     /* R/W: Mode register */
>>   #define FSI_SISC               0x8     /* R/W: Interrupt condition */
>>   #define FSI_SSTAT              0x14    /* R  : Slave status */
>> +#define FSI_SLBUS              0x30    /* W  : LBUS Ownership */
>>   #define FSI_LLMODE             0x100   /* R/W: Link layer mode register */
>>
>>   /*
>> @@ -66,6 +67,11 @@ static const int engine_page_size = 0x400;
>>   #define FSI_SMODE_LBCRR_SHIFT  8               /* Clk ratio shift */
>>   #define FSI_SMODE_LBCRR_MASK   0xf             /* Clk ratio mask */
>>
>> +/*
>> + * SLBUS fields
>> + */
>> +#define FSI_SLBUS_FORCE                0x80000000      /* Force LBUS ownership */
>> +
>>   /*
>>    * LLMODE fields
>>    */
>> @@ -981,7 +987,7 @@ static int fsi_slave_init(struct fsi_master *master, int link, uint8_t id)
>>          uint32_t cfam_id;
>>          struct fsi_slave *slave;
>>          uint8_t crc;
>> -       __be32 data, llmode;
>> +       __be32 data, llmode, slbus;
>>          int rc;
>>
>>          /* Currently, we only support single slaves on a link, and use the
>> @@ -1052,6 +1058,14 @@ static int fsi_slave_init(struct fsi_master *master, int link, uint8_t id)
>>
>>          }
>>
>> +       slbus = cpu_to_be32(FSI_SLBUS_FORCE);
>> +       rc = fsi_master_write(master, link, id, FSI_SLAVE_BASE + FSI_SLBUS,
>> +                             &slbus, sizeof(slbus));
>> +       if (rc)
>> +               dev_warn(&master->dev,
>> +                        "can't set slbus on slave:%02x:%02x %d\n", link, id,
>> +                        rc);
>> +
>>          rc = fsi_slave_set_smode(slave);
>>          if (rc) {
>>                  dev_warn(&master->dev,
>> --
>> 2.24.0
>>