Re: IDE: PDC20275 turning on/off DMA dangerous?

[Clemens Koller <clemens.koller@anagramm.de>]

Hello, Bartolmiej!

>>I am working on an embedded ppc (mpc8540) using a pretty common Promise IDE
>>PCI controller w/ a PDC20275 on it (it's called Ultra TX2).
>>I have an otherwise good Maxtor 6B120P0 (160GB) connected to it.
>>
>>But sometimes (expecially with more than zero disk-i/o-load), when I
>>turn on DMA by
>>
>>$hdparm -X69 -d1 /dev/hda
>>I get
>>
>>hda: task_out_intr: status=0x58 { DriveReady SeekComplete DataRequest }
>>ide: failed opcode was: unknown
>>hda: CHECK for good STATUS
>>
>>And when I turn off DMA with
>>$hdparm -d0 /dev/hda
>>I get sometimes a
>>
>>hda: DMA disabled
>>
>>which is fine but sometimes I also get:
>>
>>hda: status error: status=0x58 { DriveReady SeekComplete DataRequest }
>>ide: failed opcode was: unknown
>>hda: drive not ready for command
>>hda: CHECK for good STATUS
>>
>>which is not so nice.
>>Can you tell me if this is dangerous?
> 
> 
> Is there any particular reason why you are using hdparm with '-d' and '-X'?

I want to test it with DMA before fixing it into the kernel.

> Your IDE host driver (pdc202xx_new in this case) should configure
> best xfer mode and enable DMA so you shouldn't need to use hdparm.

I didn't enable automatic turning on of DMA it in the kernel by default
in the past because I had problems with this hdd controller and
interrupts (some PCI IRQ mapping issues). The interrupt issues are
solved now, so I've tried to enable DMA. DMA works pretty fine,
I was just worried about the severity of the message. It doesn't
really tell anything useful for non-ide-hackers. (whether it's
dangerous or not.)

> Given that IDE driver code for changing xfer mode and DMA setting
> is racy and actually quite hard to fix, it will probably be removed in
> the future (after auditing IDE host drivers).

So, I guess the answer is: DMA itself seems to work and it
isn't really dangerous - it's working as it's supposed to.
But if you do it the way you do, you can run into problems due
to races. Right? So, if I enable DMA as usual in the kernel,
I don't usually risk my data?!

> BTW please use linux-ide@vger.kernel.org for IDE problems

Okay, in next thread.

Thanks,
-- 
Clemens Koller
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