linux-kernel - Re: [BUG] ata: pata_marvell: Warning when probing the module

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Date:   Wed, 20 Apr 2022 20:15:07 +0800
From:   Zheyu Ma <zheyuma97@...il.com>
To:     Damien Le Moal <damien.lemoal@...nsource.wdc.com>
Cc:     Sergey Shtylyov <s.shtylyov@....ru>, linux-ide@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [BUG] ata: pata_marvell: Warning when probing the module

On Wed, Apr 20, 2022 at 11:07 AM Damien Le Moal
<damien.lemoal@...nsource.wdc.com> wrote:
>
> On 4/20/22 11:21, Zheyu Ma wrote:
> > On Wed, Apr 13, 2022 at 11:42 AM Damien Le Moal
> > <damien.lemoal@...nsource.wdc.com> wrote:
> >>
> >> On 4/12/22 15:34, Zheyu Ma wrote:
> >>> On Mon, Apr 11, 2022 at 7:53 AM Damien Le Moal
> >>> <damien.lemoal@...nsource.wdc.com> wrote:
> >>>>
> >>>> On 4/10/22 15:30, Zheyu Ma wrote:
> >>>>> Hello,
> >>>>>
> >>>>> I found a bug in the pata_marvell module.
> >>>>> When probing the driver, it seems to trigger the error path and
> >>>>> executes the function marvell_cable_detect(), but the
> >>>>> 'ap->ioaddr.bmdma_addr' is not initialized, which causes a warning.
> >>>>
> >>>> I do not have this hardware so I cannot debug this. Please debug it and
> >>>> send a patch. bmdma_addr is normally set in ata_pci_bmdma_init(), but some
> >>>> drivers set it manually in their probe functions. No idea about the
> >>>> marvell driver, I have not checked it.
> >>>
> >>> To be honest I don't have a good solution to this problem, because
> >>> other drivers don't have similar behavior. The marvell driver doesn't
> >>> even initialize 'bmdma_addr' before calling 'cable_detect'.
> >>
> >> Then this is the bug that needs to be fixed, no ?
> >>
> >>> So a simple idea I have is to check if 'bmdma_addr' is 0 before
> >>> reading it and if so return the error code ATA_CBL_NONE.
> >>
> >> And if indeed, even after it is initialized it is still 0, then yes, this
> >> change seems sensible.
> >
> > Sorry for the late reply, I found the root cause of this issue.
> > The marvell driver execute the ata_pci_bmdma_init() function, but the
> > driver just returned at the following code snippet.
> >
> > if (pci_resource_start(pdev, 4) == 0) {
> >       ata_bmdma_nodma(host, "BAR4 is zero");
> >       return;
> > }
> >
> > So the driver didn't initialize the 'bmdma_addr' but used it in the
> > cable_detect() function.
> > It seems that the problem is caused by the hardware, is this a bug
> > that we should fix?
>
> So it looks like your adapter is saying: I do not support DMA.
> In that case, having bmdma_addr as 0 should be expected and
> pata_marvel_cable_detect() should check the address before attempting an
> ioread8(). It is weird that the cable information is in that bar though...
>
> In any case, you should check the adapter specs to verify how the cable
> type can be detected. And if unknown when bmdma_addr is 0, then just
> return ATA_CBL_PATA_UNK.

Thank you very much for your detailed explanation, it helped me a lot :)

Zheyu Ma