Re: [PATCH v2 5/7] xen/arm: rcar4: add delay after programming ATU

[Mykyta Poturai <Mykyta_Poturai@xxxxxxxx>]

On 12.03.25 12:12, Grygorii Strashko wrote:
> 
> 
> On 11.03.25 12:24, Mykyta Poturai wrote:
>> From: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
>>
>> For some reason, we need a delay before accessing ATU region after
>> we programmed it. Otherwise, we'll get erroneous TLP.
>>
>> There is a code below, which should do this in proper way, by polling
>> CTRL2 register, but according to documentation, hardware does not
>> change this ATU_ENABLE bit at all.
>>
>> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
>> Signed-off-by: Mykyta Poturai <mykyta_poturai@xxxxxxxx>
>> ---
>> v1->v2:
>> * rebased
>> ---
>>   xen/arch/arm/pci/pci-designware.c | 5 +++++
>>   1 file changed, 5 insertions(+)
>>
>> diff --git a/xen/arch/arm/pci/pci-designware.c 
>> b/xen/arch/arm/pci/pci-designware.c
>> index 6ab03cf9b0..def2c12d63 100644
>> --- a/xen/arch/arm/pci/pci-designware.c
>> +++ b/xen/arch/arm/pci/pci-designware.c
>> @@ -194,6 +194,11 @@ static void 
>> dw_pcie_prog_outbound_atu_unroll(struct pci_host_bridge *pci,
>>       dw_pcie_writel_ob_unroll(pci, index, PCIE_ATU_UNR_REGION_CTRL2,
>>                                PCIE_ATU_ENABLE);
>> +    /*
>> +     * HACK: We need to delay there, because the next code does not
>> +     * work as expected on S4
>> +     */
>> +    mdelay(1);
> 
> It seems like a HACK to WA some platform issue, but in its current form it
> will affect all DW PCI compatible platforms.
> 
> So, it is required a proper solution for the affected platform to be 
> found, or
> some sort of DW PCI "quirk"s processing code be introduced.
> 
> I'd recommend to drop this patch for now from this series.
> 
>>       /*
>>        * Make sure ATU enable takes effect before any subsequent config
>>        * and I/O accesses.
> 
> BR,
> -grygorii

Hi Grygorii

After some further investigations I have retested this on V4H, and it 
seems to work fine without delays. Considering this and the issue with 
static variables and multiple PCI hosts I think I will drop ATU related 
workarounds until some proper quirks handling system is established.

-- 
Mykyta