linux-kernel - Re: [PATCH 22/40] ide-floppy: start DMA engine in idefloppy_transfer

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Date:	Tue, 20 May 2008 15:00:41 +0400
From:	Sergei Shtylyov <sshtylyov@...mvista.com>
To:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>
Cc:	linux-ide@...r.kernel.org, Borislav Petkov <petkovbb@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 22/40] ide-floppy: start DMA engine in idefloppy_transfer_pc1()

Hello.

Bartlomiej Zolnierkiewicz wrote:

> Start DMA engine and set PC_FLAG_DMA_IN_PROGRESS flag in
> idefloppy_transfer_pc1() instead of idefloppy_issue_pc()

    Good. I have long ago noticed that DMA is started too early in ide-floppy 
which is known to cobfuse some chips (like PDC20246) and was going to do a 
patch at first but the lack of hardware (and time) stopped me...

> so the Status Register and the Interrupt Reason Register
> are checked first.

> Cc: Borislav Petkov <petkovbb@...il.com>
> Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@...il.com>

> Index: b/drivers/ide/ide-floppy.c
> ===================================================================
> --- a/drivers/ide/ide-floppy.c
> +++ b/drivers/ide/ide-floppy.c
[...]
> @@ -568,6 +569,12 @@ static ide_startstop_t idefloppy_transfe
>  
>  	ide_set_handler(drive, &idefloppy_pc_intr, timeout, expiry);
>  
> +	/* Begin DMA, if necessary */
> +	if (pc->flags & PC_FLAG_DMA_OK) {
> +		pc->flags |= PC_FLAG_DMA_IN_PROGRESS;
> +		hwif->dma_ops->dma_start(drive);
> +	}
> +

    May be too early still... ide-cd does this after writing the command packet.

WBR, Sergei
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