linux-kernel - Re: spi-imx: wait_for_completion should timeout even in non-DMA transfer cases

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Date:	Mon, 21 Sep 2015 11:08:55 +0200
From:	Jean-Michel Hautbois <jean-michel.hautbois@...-labs.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	linux-spi@...r.kernel.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: spi-imx: wait_for_completion should timeout even in non-DMA
 transfer cases

2015-09-19 19:56 GMT+02:00 Mark Brown <broonie@...nel.org>:
> On Fri, Sep 18, 2015 at 02:38:27PM +0200, Jean-Michel Hautbois wrote:
>> Hi,
>>
>> I am wondering why in spi-imx the spi_imx_pio_transfer() function is
>> calling wait_for_completion() and not wait_for_completion_timeout() as
>> in the spi_imx_dma_transfer() one.
>> I can't see a good reason for this, maybe should it be calculated
>> based on the spi clock and transfer->len, or at least be the same as
>> IMX_DMA_TIMEOUT which is 3 seconds ?
>> If you want it, I have a patch, just tell me if you are interested and
>> if you prefer a calculated timeout or even something else ?
>
> A calculated timeout is probably best.

Well, it depends...
If you have a 20MHz clock, then you can transfer a byte in 4µs.
As most of the time pio_transfer is used for 8 to 32 bytes max, it
would be irrelevant to use such a small timeout.
I can obviously do it, but not sure if using a small (say, 100ms)
timeout would not be better.

JM
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