linux-kernel - Re: [PATCH v2 2/4] ata_piix: unify code for programming PIO and MWDMA timings

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Date:	Fri, 14 Oct 2011 20:43:16 +0400
From:	Sergei Shtylyov <sshtylyov@...sta.com>
To:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
CC:	Jeff Garzik <jgarzik@...ox.com>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] ata_piix: unify code for programming PIO and MWDMA
 timings

Hello.

On 10/14/2011 05:43 PM, Bartlomiej Zolnierkiewicz wrote:

>>> From: Bartlomiej Zolnierkiewicz<bzolnier@...il.com>
>>> Subject: [PATCH v2] ata_piix: unify code for programming PIO and MWDMA timings

>>> Besides making things noticably simpler it results in ~2% decrease in
>>> the driver LOC count and also ~2% decrease in the driver binary size
>>> (as measured on x86-32).

>>> Fix piix_set_piomode() documentation while at it.

>>> Signed-off-by: Bartlomiej Zolnierkiewicz<bzolnier@...il.com>

>>      I'm still inclined to NAK this patch.

>>> ---
>>> v2: remove use_mwdma variable and fix comment style

>>> earlier references:
>>> https://lkml.org/lkml/2011/2/8/99

>>>    drivers/ata/ata_piix.c |  111 ++++++++++++++++---------------------------------
>>>    1 file changed, 38 insertions(+), 73 deletions(-)

>>> Index: b/drivers/ata/ata_piix.c
>>> ===================================================================
>>> --- a/drivers/ata/ata_piix.c
>>> +++ b/drivers/ata/ata_piix.c
>> [...]
>>> @@ -811,31 +822,20 @@ static void do_pata_set_dmamode(struct a
>> [...]
>>> -	if (ap->udma_mask)
>>> -		pci_read_config_byte(dev, 0x48,&udma_enable);

>>      Don't think you should remove this.

>>> -
>>>    	if (speed>= XFER_UDMA_0) {
>>> -		unsigned int udma = adev->dma_mode - XFER_UDMA_0;
>>> +		unsigned int udma = speed - XFER_UDMA_0;
>>>    		u16 udma_timing;
>>>    		u16 ideconf;
>>>    		int u_clock, u_speed;
>>>
>>> +		spin_lock_irqsave(&piix_lock, flags);
>>> +
>>> +		pci_read_config_byte(dev, 0x48,&udma_enable);

>>      But you should also clear the UDMA enable bit when setting an MWDMA mode, no?

>>> +
>>>    		/*
>>>    		 * UDMA is handled by a combination of clock switching and
>>>    		 * selection of dividers
>>> @@ -868,56 +868,21 @@ static void do_pata_set_dmamode(struct a
>>>    			   performance (WR_PingPong_En) */
>>>    			pci_write_config_word(dev, 0x54, ideconf);
>>>    		}
>>> +
>>> +		pci_write_config_byte(dev, 0x48, udma_enable);
>>> +
>>> +		spin_unlock_irqrestore(&piix_lock, flags);
>>>    	} else {
>>> -		/*
>>> -		 * MWDMA is driven by the PIO timings. We must also enable
>>> -		 * IORDY unconditionally along with TIME1. PPE has already
>>> -		 * been set when the PIO timing was set.
>>> -		 */
>>> -		unsigned int mwdma	= adev->dma_mode - XFER_MW_DMA_0;
>>> -		unsigned int control;
>>> -		u8 slave_data;
>>> +		/* MWDMA is driven by the PIO timings. */
>>> +		unsigned int mwdma = speed - XFER_MW_DMA_0;
>>>    		const unsigned int needed_pio[3] = {
>>>    			XFER_PIO_0, XFER_PIO_3, XFER_PIO_4
>>>    		};
>>>    		int pio = needed_pio[mwdma] - XFER_PIO_0;

>> [...]
>>> -		if (ap->udma_mask)
>>> -			udma_enable&= ~(1<<   devid);

>>      Still don't understand why you're removing this code.

>>> -
>>> -		pci_write_config_word(dev, master_port, master_data);
>>> +		/* XFER_PIO_0 is never used currently */
>>> +		piix_set_timings(ap, adev, pio);
>>>    	}
>>> -	/* Don't scribble on 0x48 if the controller does not support UDMA */
>>> -	if (ap->udma_mask)
>>> -		pci_write_config_byte(dev, 0x48, udma_enable);

>>      Should have kept this one too...

> We still have following code at the end of piix_set_timings():
>
> 	/* Ensure the UDMA bit is off - it will be turned back on if
> 	   UDMA is selected */
>
> 	if (ap->udma_mask) {
> 		pci_read_config_byte(dev, 0x48,&udma_enable);
> 		udma_enable&= ~(1<<  (2 * ap->port_no + adev->devno));
> 		pci_write_config_byte(dev, 0x48, udma_enable);
> 	}

> so everything should be OK.

    Ah, I should have looked... Didn't expect it to be there, and it in fact 
shouldn't be there, but now I'm OK with your patch. :-)

WBR, Sergei
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