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Message-ID: <493D0CB8.3060900@ru.mvista.com>
Date: Mon, 08 Dec 2008 15:02:00 +0300
From: Sergei Shtylyov <sshtylyov@...mvista.com>
To: Shane McDonald <mcdonald.shane@...il.com>
Cc: bzolnier@...il.com, linux-ide@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Resurrect IT8172 IDE controller driver
Hello.
Shane McDonald wrote:
> I have made some of the required changes, but I have some questions.
> See in-line for my resolution / questions for each comment.
>
> On Mon, Nov 24, 2008 at 4:33 AM, Sergei Shtylyov
> <sshtylyov@...mvista.com> wrote:
>
>> Hello.
>>
>> Shane McDonald wrote:
>>
>>
>>> diff -uprN a/drivers/ide/it8172.c b/drivers/ide/it8172.c
>>> --- a/drivers/ide/it8172.c 1969-12-31 18:00:00.000000000 -0600
>>> +++ b/drivers/ide/it8172.c 2008-11-23 01:06:01.000000000 -0600
>>> @@ -0,0 +1,205 @@
>>> +/*
>>> + *
>>> + * BRIEF MODULE DESCRIPTION
>>> + * IT8172 IDE controller support
>>> + *
>>> + * Copyright 2000 MontaVista Software Inc.
>>> + * Author: MontaVista Software, Inc.
>>> + * stevel@...sta.com or source@...sta.com
>>>
>>>
>> You can remove the former address, Steve Longerbeam is no longer with MV
>> (quit long ago). And I think you may add your own copyright now.
>>
>
> OK, I will update accordingly.
>
>
>>> +/*
>>> + * Prototypes
>>> + */
>>>
>> I see no prototypes here...
>>
>
> Ah yes, the prototypes were removed, but not the comment. I will remove this.
>
>
>>> +static void it8172_set_pio_mode(ide_drive_t *drive, const u8 pio)
>>> +{
>>> + ide_hwif_t *hwif = HWIF(drive);
>>> + struct pci_dev *dev = to_pci_dev(hwif->dev);
>>> + int is_slave = (&hwif->drives[1] == drive);
>>>
>> Use simpler "drive->dn & 1" (and drop the useless parens please) -- & can
>> be dropped though as the controller has only a single channel...
>>
>
> I don't believe it can be dropped entirely -- although the
> controller only has a single channel, it does support two drives on
> that channel. Unless I understand incorrectly, I will make the
> "drive->dn & 1" change.
>
Believe it or not, drive->dn will be 0 or 1 in this case, so & is
superfluous. :-)
I don't insist on dropping it though...
>>> + /*
>>> + * Enable port 0x44. The IT8172 spec is confused; it calls
>>> + * this register the "Slave IDE Timing Register", but in fact,
>>> + * it controls timing for both master and slave drives.
>>> + */
>>> + drive_enables |= 0x4000;
>>>
>> This is strange because this IDE controller seems to be a clone of the one
>> in the Intel PIIX chip. However, the spec. I have tellm it's not an exact
>> clone.
>>
I just don't undestand what this bit is good for in IT8172G...
Perhaps by clearing it once could achieve PIO0 timings, just like by
clearing the fast timing bits on PIIX?
>> I suggest that you take a close look at drivers/ide/piix.c...
>>
>
> The specs I have indicate that it is not the same. For example, bits
> 13:12 in the IDETIM register at offset 0x40-0x41 of the PIIX give the
> IORDY Sample Point, but the same function is found in bits 19-17 in
> the SLVT register at offset 0x44-0x47 in the IT8172. Perhaps better
> comments are in order, or perhaps these bitfields should be defined in
> a .h file?
>
No, IT8172G just implements them differently. But you can still find
in this driver a good example of how things should be done...
>>> + if (is_slave) {
>>> + drive_enables &= 0xc006;
>>> + if (pio > 1)
>>> + /* enable prefetch and IORDY sample-point */
>>> + drive_enables |= 0x0060;
>>>
>> IORDY sampling shouldn't be enabled for PIO mode 2 always, only if the
>> drive supports it.
>> Prefetch should only be enabled for ATA disks, not the ATAPI devices
>>
>
> OK, I will update accordingly. Am I correct that prefetch should be
> enabled if "drive->media == ide_disk", and not otherwise?
>
Yes, you're correct.
> I am not sure how to determine if IORDY sampling is supported by a
>
I think Bart has replied to thia already...
> drive. If I'm reading the code correctly, other drivers only check
> that the PIO mode is > 2 (not > 1 as in my driver) -- that seems to be
> the case for at least piix.c, siimage.c, and it8213.c.
>
That's because PIO modes above 2 necessiate IORDY, while for mode 2
the drive can require it optionally.
>>> +static void it8172_set_dma_mode(ide_drive_t *drive, const u8 speed)
>>> +{
>>> + ide_hwif_t *hwif = HWIF(drive);
>>> + struct pci_dev *dev = to_pci_dev(hwif->dev);
>>> + int a_speed = 3 << (drive->dn * 4);
>>> + int u_flag = 1 << drive->dn;
>>> + int u_speed = 0;
>>> + u8 reg48, reg4a;
>>> +
>>> + const u8 mwdma_to_pio[] = { 0, 3, 4 };
>>> + u8 pio;
>>> +
>>> + pci_read_config_byte(dev, 0x48, ®48);
>>> + pci_read_config_byte(dev, 0x4a, ®4a);
>>> +
>>> + if (speed >= XFER_UDMA_0) {
>>> +
>>> + /* Setting the DMA cycle time to 2 or 3 PCI clocks
>>> + * (60 and 91 nsec at 33 MHz PCI clock) seems to cause
>>> + * BadCRC errors during DMA transfers on some drives,
>>>
>> Sigh, such drives should have been blacklisted...
>>
>
> Do you think I should keep this code in here? It kind of seems silly
> to run drivers at UDMA0 speeds just because of a few bad drives back
> in 2000 when the driver was originally written.
If was only happening for some drives, you probably shouldn't keep it...
> Should this not be
> handled in userspace by hdparm? Other drivers don't seem to do
> something similar.
>
This is usually handled by blacklisting the drives for the user's
convenience.
>>> + * even though both numbers meet the minimum ATAPI-4 spec
>>> + * of 73 and 54 nsec for UDMA 1 and 2 respectively.
>>> + * So the faster times are not implemented here.
>>> + * The good news is that the slower cycle time has
>>> + * very little affect on transfer performance.
>>>
>> This should only affect the write performance, reads.
>>
"On reads the drive dictatees the timings" I was going to write. :-)
>>> +static unsigned int __devinit init_chipset_it8172(struct pci_dev *dev)
>>> +{
>>> + unsigned char progif;
>>> +
>>> + /*
>>> + * Place both IDE interfaces into PCI "native" mode
>>> + */
>>> + pci_read_config_byte(dev, PCI_CLASS_PROG, &progif);
>>> + pci_write_config_byte(dev, PCI_CLASS_PROG, progif | 0x05);
>>> +
>>> + return dev->irq;
>>> +}
>>>
>>>
>> As Alan have said, you can't do that here.
>>
>
> I will remove this.
>
You'll probably need to add this as a quirk to drivers/pci/quirks.c
-- unless the bootloader sets the controller to native mode itself.
>>> +static const struct ide_port_info it8172_chipset __devinitdata = {
>>> + .name = DRV_NAME,
>>> + .init_chipset = init_chipset_it8172,
>>> + .port_ops = &it8172_port_ops,
>>> + .enablebits = {{0x00, 0x00, 0x00}, {0x40, 0x00, 0x01} },
>>>
>>>
>> Wrong, should be:
>>
>> .enablebits = {{0x41, 0x80, 0x80}, {0x00, 0x00, 0x00}},
>>
>> If that doesn't work (firmware doesn't enable the channel), you can leave
>> it all 0s...
>>
Er, I was wrong here -- you actiually can't do that as the channel
will remain disabled.
> Well, mine is clearly wrong. Am I correct that {0x41, 0x80, 0x80} is
> checking that the IDE Decode Enable bit is set? This bit is in the
> same location in both the PIIX and the IT8172.
>
Yes, you're correct. You should add the code to force it enabled if
the bootloader doesn't do that.
>>> .host_flags = IDE_HFLAG_SINGLE,
>>> + .pio_mask = ATA_PIO4,
>>>
I'm not seeing how PIO mode 0 is supportable.
>>> + .swdma_mask = ATA_SWDMA2_ONLY,
>>>
The SWDMA support could be dropped altogether -- these modes are slow
and long obsolete.
>>> + .mwdma_mask = ATA_MWDMA12_ONLY,
>>>
>> More modes are supportable...
>>
>
> I will update accordingly.
>
These masks were stolen from the piix.c driver and are determined by
the limitation of the timing register fileds being only 2-bit wide.
IT8172G has these bits implemented differently, hence the limitation
shouldn't apply. You shouldn't just update the masks without doing
anythiung about programming the modes...
>>> +MODULE_AUTHOR("SteveL@...sta.com");
>>>
>> I wonder why Steve didn't specify his full name... :-)
>>
>
> I will change this to my name.
>
I don't think it would be a legitimate change...
> Thank you for your time!
>
If you could give me more free time instead... :-)
MBR, Sergei
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