linux-kernel - Re: 2.6.29-rc libata sff 32bit PIO regression

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Date:	Sat, 31 Jan 2009 18:11:50 +0300
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Hugh Dickins <hugh@...itas.com>, Jeff Garzik <jgarzik@...hat.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.29-rc libata sff 32bit PIO regression

Hello.

Alan Cox wrote:

> pata_amd: Program FIFO
>
> From: Alan Cox <alan@...rguk.ukuu.org.uk>
>
> With 32bit PIO we can use the posted write buffers, but only for 32bit I/O
> cycles. This means we must disable the FIFO for ATAPI where a final 16bit
> cycle may occur.
>
> Rework the FIFO logic so that we disable the FIFO then selectively re-enable
> it when we set the timings on AMD devices. Also fix a case where we scribbled
> on PCI config 0x41 of Nvidia chips when we shouldn't.
>
> Signed-off-by: Alan Cox <alan@...rguk.ukuu.org.uk>
>   
[...]
> diff --git a/drivers/ata/pata_amd.c b/drivers/ata/pata_amd.c
> index 63719ab..c380a4e 100644
> --- a/drivers/ata/pata_amd.c
> +++ b/drivers/ata/pata_amd.c
>   
[...]
> @@ -158,6 +165,40 @@ static int amd_cable_detect(struct ata_port *ap)
>  }
>  
>  /**
> + *	amd_fifo_setup		-	set the PIO FIFO for ATA/ATAPI
> + *	@ap: ATA interface
> + *	@adev: ATA device
> + *
> + *	Set the PCI fifo for this device according to the devices present
> + *	on the bus at this point in time. We need to turn the post write buffer
> + *	off for ATAPI devices as we may need to issue a word sized write to the
> + *	device as the final I/O
> + */
> +
> +static void amd_fifo_setup(struct ata_port *ap)
> +{
> +	struct ata_device *adev;
> +	struct pci_dev *pdev = to_pci_dev(ap->host->dev);
> +	static const u8 fifobit[2] = { 0xC0, 0x30};
> +	u8 fifo = fifobit[ap->port_no];
> +	u8 r;
> +
> +
> +	ata_for_each_dev(adev, &ap->link, ENABLED) {
> +		if (adev->class == ATA_DEV_ATAPI)
> +			fifo = 0;
> +	}
>   

   Er, couldn't we do that dynamically, based on which device is 
executing the command now?

> +	if (pdev->device == PCI_DEVICE_ID_AMD_VIPER_7411) /* FIFO is broken */
> +		fifo = 0;
> +
> +	/* On the later chips the read prefetch bits become no-op bits */
> +	pci_read_config_byte(pdev, 0x41, &r);
> +	r &= ~fifobit[ap->port_no];
>   

  Why not:

       r &= ~fifo;

> +	r |= fifo;
> +	pci_write_config_byte(pdev, 0x41, r);
> +}

MBR, Sergei


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