linux-kernel - Re: [PATCH 1/3] ata: sata_dwc_460ex: use "dmas" DT property to find dma channel

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Date:	Sat, 19 Dec 2015 18:56:57 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Måns Rullgård <mans@...sr.com>
Cc:	Julian Margetson <runaway@...dw.ms>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	Tejun Heo <tj@...nel.org>, linux-ide@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] ata: sata_dwc_460ex: use "dmas" DT property to find
 dma channel

On Sat, Dec 19, 2015 at 5:40 PM, Måns Rullgård <mans@...sr.com> wrote:

> OK, I've found something.  The dma setup errors are benign, caused by
> the driver calling dmaengine_prep_slave_sg() even for non-dma
> operations.

I suppose the following is a quick fix to avoid preparing descriptor
for non-DMA operations (not tested anyhow)

a/drivers/ata/sata_dwc_460ex.c
+++ b/drivers/ata/sata_dwc_460ex.c
@@ -1041,6 +1041,9 @@ static void sata_dwc_qc_prep_by_tag(struct
ata_queued_cmd *qc, u8 tag)
                __func__, ap->port_no, get_dma_dir_descript(qc->dma_dir),
                 qc->n_elem);

+       if (!is_slave_direction(qc->dma_dir))
+               return;
+
        desc = dma_dwc_xfer_setup(qc);
        if (!desc) {
                dev_err(ap->dev, "%s: dma_dwc_xfer_setup returns NULL\n",

> The real error is the lock recursion that's reported
> later.  I wasn't seeing it since I was running a UP non-preempt kernel.
> With lock debugging enabled, I get the same error.  This patch should
> fix it.

> -       spin_lock_irqsave(&ap->host->lock, flags);
>         hsdevp->cmd_issued[tag] = cmd_issued;
> -       spin_unlock_irqrestore(&ap->host->lock, flags);

> +

This will create a second empty line, though I don't care it is so minor.

-- 
With Best Regards,
Andy Shevchenko
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