Re: [PATCH v2 2/4] ata_piix: unify code for programming PIO and MWDMAtimings

[Sergei Shtylyov]

Hello.

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

> > > From: Bartlomiej Zolnierkiewicz<bzolnier@xxxxxxxxx>
> > > 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@xxxxxxxxx>

> >      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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