netdev - Re: [PATCH] stmmac: extend DMA initialization delay to 2.5 seconds

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Date:	Thu, 05 Jun 2014 15:24:59 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	Alexey.Brodkin@...opsys.com
Cc:	netdev@...r.kernel.org, hdegoede@...hat.com,
	peppe.cavallaro@...com, wens@...e.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
	Vineet.Gupta1@...opsys.com
Subject: Re: [PATCH] stmmac: extend DMA initialization delay to 2.5 seconds

From: Alexey Brodkin <Alexey.Brodkin@...opsys.com>
Date: Thu,  5 Jun 2014 16:58:00 +0400

> On some platforms existing 100 msecond delay is not enough for DMA block to
> recover after reset. This is because MAC DMA waits for all PHY input clocks
> to present and depending on the board reset bit deassertion may take much
> longer than previously used 100 milliseconds
> 
> I have a board that requires more than 2 seconds for DMA to zero "reset" bit.
> If for other boards it's still not long enough this value should be extended
> once again.
> 
> In the same change I convert "mdelay" to "msleep" to make CPU available for
> other processes during DMA init delay which is especially useful in case of
> delay for a few seconds.
> 
> Signed-off-by: Alexey Brodkin <abrodkin@...opsys.com>

This will not work, you cannot sleep with spinlocks held, and this code is
absolutely called in such a context.

For example stmmac_resume() --> stmmac_hw_setup() -> stmmac_init_dma_engine().

stmmac_resume() holds priv->lock over all of these operations, and even has
interrupts disabled.
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