Re: [Qemu-devel] [PATCHv2] esp: Do not overwrite ESP_TCHI after reset

[Hannes Reinecke]

On 11/11/2014 01:37 PM, Paolo Bonzini wrote:
> 
> 
> On 10/11/2014 21:11, Hannes Reinecke wrote:
>> On 11/10/2014 07:32 PM, Paolo Bonzini wrote:
>>> On 10/11/2014 16:52, Hannes Reinecke wrote:
>>>> After a reset ESP_TCHI should contain the unique ID
>>>> of the chip. This value will be overwritten with the
>>>> current tranfer count if the transfer count has
>>>> previously been set.
>>>> So we should always return the chip id if ESP_TCHI
>>>> has never been written to.
>>>
>>> What if ESP_TCHI was written 0?  Why should it return the chip id?
>>>
>> It's a complex thing. The documentation says 'ESP_TCHI returns the chip
>> id until been written to'.
>> And ESP_TCHI is strictly speaking only valid if the 'Features enabled'
>> bit is set in ESP_CFG2. (Not that the driver checks this).
>> To handle it correctly we would need to add a flag whenever ESP_TCHI
>> is written to, but I thought it'd be slightly too much.
> 
> I'm worried that the chip_id will reappear if you write a low (<65536)
> value to ESP_TCLOW/MED/HI.
> 
> Adding the flag is just a couple lines more than this patch, let's do it
> right.
> 
Right.

Will be sending an updated patch.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                   zSeries & Storage
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