Re: [PATCH v6 10/13] vpci/header: reset the command register when adding devices

[Oleksandr Andrushchenko <Oleksandr_Andrushchenko@xxxxxxxx>]

On 04.02.22 16:30, Jan Beulich wrote:
> On 04.02.2022 07:34, Oleksandr Andrushchenko wrote:
>> Reset the command register when assigning a PCI device to a guest:
>> according to the PCI spec the PCI_COMMAND register is typically all 0's
>> after reset.
> It's not entirely clear to me whether setting the hardware register to
> zero is okay. What wants to be zero is the value the guest observes
> initially.
"the PCI spec says the PCI_COMMAND register is typically all 0's after reset."
Why wouldn't it be ok? What is the exact concern here?
>> --- a/xen/drivers/vpci/header.c
>> +++ b/xen/drivers/vpci/header.c
>> @@ -454,8 +454,7 @@ static void cmd_write(const struct pci_dev *pdev, 
>> unsigned int reg,
>>           pci_conf_write16(pdev->sbdf, reg, cmd);
>>   }
>>   
>> -static void guest_cmd_write(const struct pci_dev *pdev, unsigned int reg,
>> -                            uint32_t cmd, void *data)
>> +static uint32_t emulate_cmd_reg(const struct pci_dev *pdev, uint32_t cmd)
> The command register is a 16-bit one, so parameter and return type should
> either be plain unsigned int (preferred, see ./CODING_STYLE) or uint16_t
> imo.
God catch, thank you
> Jan
>
Thank you,
Oleksandr