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Re: [Qemu-devel] [PATCHv2] esp: Do not overwrite ESP_TCHI after reset
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCHv2] esp: Do not overwrite ESP_TCHI after reset |
Date: |
Tue, 11 Nov 2014 13:37:17 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0 |
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