From: Vitaly Wool <vwool@ru.mvista.com>
To: David Brownell <david-b@pacbell.net>
Cc: spi-devel-general@lists.sourceforge.net, Greg KH <greg@kroah.com>,
linux-kernel@vger.kernel.org, dpervushin@gmail.com,
akpm@osdl.org, basicmark@yahoo.com, komal_shah802003@yahoo.com,
stephen@streetfiresound.com, Joachim_Jaeger@digi.com
Subject: Re: [spi-devel-general] Re: [PATCH/RFC] SPI: add DMAUNSAFE analog
Date: Fri, 16 Dec 2005 01:17:56 +0300 [thread overview]
Message-ID: <43A1EB94.5040300@ru.mvista.com> (raw)
In-Reply-To: <200512151206.26515.david-b@pacbell.net>
David Brownell wrote:
>On Wednesday 14 December 2005 10:47 pm, Vitaly Wool wrote:
>
>
>
>>One cannot allocate memory in interrupt context, so the way to go is
>>allocating it on stack, thus the buffer is not DMA-safe.
>>
>>
>
>kmalloc(..., GFP_ATOMIC) is the way to allocate memory in irq context.
>It's done that way throughout the kernel.
>
>
It's not applicable within the RT-related changes. kmalloc anyway takes
mutexes, so allocationg it in interrupt context is buggy.
*Legacy* kernel code does that but why produce a new code with that?
>
>
>
>>Making it DMA-safe in thread that does the very message processing is a
>>good way of overcoming this.
>>
>>
>
>The rest of Linux appears to work fine without needing such mechanisms...
>
>
The rest of Linux still has a lot of bugs. Noone I guess is ready to
argue that.
>I really fail to see why you think SPI needs that. USB isn't the only
>counterexample, but it's particularly relevant since both USB and SPI
>use asynchronous message passing over serial links ... and USB has a
>rather complete driver stack over it. (None of the USB based WLAN
>drivers need those static buffers you worry about, by the way...)
>
>
I haven't heard of USB device registers needing to be written in IRQ
context. I'm not that well familiar with USB, so if you give such an
example, that'd be fine.
>>Using preallocated buffer is not a good way, since it may well be
>>already used by another interrupt or not yet processed by the worker
>>thread (or tasklet, or whatever).
>>
>>
>
>We would call those "driver bugs" and expect patches. :)
>
>
>
Well, I know one such patch ;)
>>One can not predict how many transfers are
>>gonna be dropped due to "previous trransfer is being processed" problem,
>>it depends on the system load. And though it's not a problem for
>>touchscreen, it *will* be a problem if it were MMC, for instance.
>>
>>
>
>Huh, well I've already seen one nice "mmc/sd over SPI" driver, using
>a slightly earlier version of the framework than is found in mm3.
>It's being used for root filesystems.
>
>So demonstrably there is no problem for MMC/SD, either.
>
>
No problem... Has the driver been tested in stress conditions? If not,
then I guess you can't say this for sure :)
Vitaly
next prev parent reply other threads:[~2005-12-15 22:18 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-12-12 15:20 [PATCH 2.6-git 0/4] SPI core refresh Vitaly Wool
2005-12-12 15:22 ` [PATCH 2.6-git 1/4] SPI core refresh: SPI core patch Vitaly Wool
2005-12-12 15:49 ` Russell King
2005-12-12 15:24 ` [PATCH 2.6-git 2/4] SPI core refresh: MTD dataflash driver Vitaly Wool
2005-12-12 15:26 ` [PATCH 2.6-git 3/4] SPI core refresh: SPI/PNX controller Vitaly Wool
2005-12-12 15:27 ` [PATCH 2.6-git 4/4] SPI core refresh: dumb EEPROM driver Vitaly Wool
2005-12-12 18:01 ` [PATCH 2.6-git 0/4] SPI core refresh Rui Sousa
2005-12-13 12:09 ` [spi-devel-general] " dmitry pervushin
2005-12-13 15:11 ` Rui Sousa
2005-12-13 17:06 ` dmitry pervushin
2005-12-14 6:57 ` Vitaly Wool
2005-12-14 14:28 ` Rui Sousa
2005-12-13 16:35 ` David Brownell
2005-12-13 18:02 ` Rui Sousa
2005-12-13 14:06 ` [PATCH/RFC] SPI: add async message handing library to David Brownell's core Vitaly Wool
2005-12-13 16:53 ` [PATCH/RFC] SPI: add DMAUNSAFE analog " Vitaly Wool
2005-12-13 19:01 ` David Brownell
2005-12-13 19:15 ` Greg KH
2005-12-14 13:50 ` Vitaly Wool
2005-12-14 17:18 ` Greg KH
2005-12-14 17:53 ` Vitaly Wool
2005-12-14 18:50 ` [PATCH/RFC] SPI: add DMAUNSAFE analog David Brownell
2005-12-14 19:29 ` Vitaly Wool
2005-12-14 19:02 ` [PATCH/RFC] SPI: add DMAUNSAFE analog to David Brownell's core David Brownell
2005-12-14 19:19 ` Vitaly Wool
2005-12-14 19:33 ` [spi-devel-general] Re: [PATCH/RFC] SPI: add DMAUNSAFE analog David Brownell
2005-12-14 19:34 ` [PATCH/RFC] SPI: add DMAUNSAFE analog to David Brownell's core Vitaly Wool
2005-12-15 6:47 ` Vitaly Wool
2005-12-15 16:44 ` Greg KH
2005-12-15 22:23 ` Vitaly Wool
2005-12-15 23:02 ` Greg KH
2005-12-16 8:37 ` Vitaly Wool
2005-12-16 17:34 ` Greg KH
2005-12-16 18:32 ` [spi-devel-general] Re: [PATCH/RFC] SPI: add DMAUNSAFE analog David Brownell
2005-12-15 20:06 ` David Brownell
2005-12-15 22:17 ` Vitaly Wool [this message]
2005-12-15 22:33 ` Greg KH
2005-12-16 3:34 ` Andy Isaacson
2005-12-16 5:17 ` Greg KH
2005-12-14 19:16 ` [PATCH/RFC] SPI: add DMAUNSAFE analog to David Brownell's core Greg KH
2005-12-14 19:30 ` Vitaly Wool
2005-12-15 10:00 ` [spi-devel-general] " dmitry pervushin
2005-12-14 17:22 ` David Brownell
2005-12-14 17:50 ` Vitaly Wool
2005-12-14 19:17 ` [PATCH/RFC] SPI: add DMAUNSAFE analog David Brownell
2005-12-14 20:11 ` Vitaly Wool
2005-12-13 21:47 ` [PATCH/RFC] SPI: add DMAUNSAFE analog to David Brownell's core Vitaly Wool
2005-12-13 22:15 ` Vitaly Wool
2005-12-14 16:55 ` David Brownell
2005-12-14 17:23 ` Vitaly Wool
2005-12-14 18:48 ` [PATCH/RFC] SPI: add async message handing library " Stephen Street
2005-12-14 19:41 ` Vitaly Wool
2005-12-14 21:19 ` Stephen Street
2005-12-14 19:31 ` [PATCH/RFC] SPI: add async message handing library David Brownell
2005-12-15 12:19 ` [PATCH/RFC] SPI: async message handing library update Vitaly Wool
2005-12-18 18:59 ` David Brownell
2005-12-19 15:40 ` [spi-devel-general] " dmitry pervushin
2005-12-20 7:23 ` David Brownell
2005-12-20 18:02 ` Vitaly Wool
2005-12-22 17:28 ` David Brownell
2005-12-22 22:10 ` Vitaly Wool
2005-12-22 23:55 ` David Brownell
2005-12-21 13:17 ` Vitaly Wool
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