linux-kernel - Re: Need help to debug ata errors

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Message-ID: <3aba2b93-9440-e581-61aa-76161f55563f@xilinx.com>
Date:   Mon, 6 Dec 2021 11:18:07 +0000
From:   Ayan Kumar Halder <ayan.kumar.halder@...inx.com>
To:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Ayan Kumar Halder <ayan.kumar.halder@...inx.com>,
        <linux-ide@...r.kernel.org>
CC:     <axboe@...nel.dk>, <linux-kernel@...r.kernel.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Stefano Stabellini <stefano.stabellini@...inx.com>
Subject: Re: Need help to debug ata errors

Hi Damien,

Thanks a lot for your inputs.

On 06/12/2021 00:12, Damien Le Moal wrote:
> On 2021/12/03 20:11, Ayan Kumar Halder wrote:
>> Hi All,
>>
>> I am trying to run linux as a DomU guest on Xen with AHCI assigned to it.
>> I can confirm that SATA works (ie able to detect sdb) as a Dom0 guest.
>> However, it does not work as a DomU guest.
>>
>> Hardware :- ZCU102 board and it has two sata ports
>> Kernel :- 5.10
>>
>> I have enabled the debug logs in drivers/ata
>>
>> 1. Logs from dom0 (where SATA works) https://pastebin.com/2BhMDq47
>> 2. Logs from domU (where SATA does not work) https://pastebin.com/fE8WZnZ0
>>
>> Can some help me to answer these questions
>> 1. What does this mean "1st FIS failed" ?
>>
>> 2. In the dom0 logs, PORT_SCR_ERR = 0x41d0002 whereas in domU logs,
>> PORT_SCR_ERR = 0. Does it give some hints ?
>>
>> 3. Any other issues or hints to debug this ?
>>
>> I can confirm that in domU scenario, we do not get any interrupts from
>> the device. What might be going wrong here ?
> 
> That would be the first thing to check since without interrupts you will not get
> any command completion. Commands will timeout and probe will not work.
> And this IRQ problem is Xen territory, not ata.

I am actually debugging the interrupts from the Xen's side. I can 
confirm that do_IRQ() (Xen's irq handler) does not receive AHCI 
interrupts. It does get invoked for interrupts from serial and other 
devices.

I have seen commands being timed out which is due to the iRQ issue. But 
suprisingly, ahci probe is successful.
> 
> The 1st FIS failed error may be due to some problems with AHCI PCI bar/register
> accesses, which may not be working. This I think points again to Xen setup with
> domU, which may not have the necessary access rights to get IRQ and PCI bar
> accesses ? (I have no experience with Xen)

This is the device tree https://pastebin.com/HtdLx63v . I think it is 
not related to PCI bus. Please correct me if mistaken.

I have the necessary debug support from Xen. Can you let me know what 
bits I can debug from SATA side (for eg reading a particular register) 
which will confirm if SATA has been programmed correctly or not ?

- Ayan

> 
>>
>> Thanks in advance.
>>
>> Kind regards,
>> Ayan
>>
> 
>