Re: [RFC 21/24] xen/arm: vexpress: Blacklist a list of board specific devices

[Julien Grall <julien.grall@linaro.org>]

On 08/22/2013 03:00 PM, Ian Campbell wrote:
> On Fri, 2013-08-16 at 22:05 +0100, Julien Grall wrote:
>> On Versatile there is a bunch of devices that must not pass-through to any
> 
> "there are a bunch of devices which must not be passed-through"
> 
>> guest (power management and cache coherency devices).
>>
>> This commit also blacklist the HDLCD device because then is unable to correctly
>                                                           ^Linux?
> 
>> map the framebuffer. Therefore, when Linux will try to access to the framebuffer,
>> Xen will receive a non-handled data access.
> 
> Can/should this be conditional on whether Xen has console=hdlcd or not?
> Or does Xen use the device unconditionally if it exists? TBH I think it
> would be normal to prefer that Linux gets this device...
> 
> (I'm unclear how this relates to memreserve as mention in the code
> comment)

This issue is only when the HDLCD is used by Linux (not Xen). To specify
where the framebuffer lives in the memory, there is a property
"framebuffer" which contains address/size.
This regions must be reserved to avoid Linux/u-boot play with it. So the
DTS has a memreserve range with the same value. I don't really
understand all memreserve things but Xen must cope with it.

If this device is mapped, Xen will receive a data abort because Linux
can't access to the framebuffer.

This solution is not upstream (only in the Linaro tree). I don't know if
this driver works with the vanilla kernel.

> 
>>
>> Signed-off-by: Julien Grall <julien.grall@linaro.org>
>> ---
>>  xen/arch/arm/platforms/vexpress.c |   17 +++++++++++++++++
>>  1 file changed, 17 insertions(+)
>>
>> diff --git a/xen/arch/arm/platforms/vexpress.c b/xen/arch/arm/platforms/vexpress.c
>> index 8fc30c4..ece7bd9 100644
>> --- a/xen/arch/arm/platforms/vexpress.c
>> +++ b/xen/arch/arm/platforms/vexpress.c
>> @@ -125,9 +125,26 @@ static const char const *vexpress_dt_compat[] __initdata =
>>      NULL
>>  };
>>  
>> +static const struct dt_device_match vexpress_blacklist_dev[] __initconst =
>> +{
>> +    /* Cache Coherent Interconnect */
>> +    DT_MATCH_COMPATIBLE("arm,cci-400"),
>> +    DT_MATCH_COMPATIBLE("arm,cci-400-pmu"),
>> +    /* Video device
>> +     * TODO: remove it once memreserve is handled properly by Xen
>> +     */
>> +    DT_MATCH_COMPATIBLE("arm,hdlcd"),
>> +    /* Hardware power management */
>> +    DT_MATCH_COMPATIBLE("arm,vexpress-reset"),
>> +    DT_MATCH_COMPATIBLE("arm,vexpress-reboot"),
>> +    DT_MATCH_COMPATIBLE("arm,vexpress-shutdown"),
>> +    { /* sentinel */ },
>> +};
>> +
>>  PLATFORM_START(vexpress, "VERSATILE EXPRESS")
>>      .compatible = vexpress_dt_compat,
>>      .reset = vexpress_reset,
>> +    .blacklist_dev = vexpress_blacklist_dev,
>>  PLATFORM_END
>>  
>>  /*
> 
> 


-- 
Julien Grall