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

[Paolo Bonzini <pbonzini@redhat.com>]

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.

Paolo