linux-kernel - Re: [PATCH v4] drivers/block/mtip32xx: Adding new driver mtip32xx

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Message-ID: <4E8632BB.20700@fusionio.com>
Date:	Fri, 30 Sep 2011 15:20:59 -0600
From:	Jens Axboe <jaxboe@...ionio.com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	"Sam Bradshaw (sbradshaw)" <sbradshaw@...ron.com>,
	"alan@...rguk.ukuu.org.uk" <alan@...rguk.ukuu.org.uk>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Jeff Garzik <jgarzik@...ox.com>,
	"jmoyer@...hat.com" <jmoyer@...hat.com>,
	"Asai Thambi Samymuthu Pattrayasamy (asamymuthupa) [CONTRACTOR]" 
	<asamymuthupa@...ron.com>
Subject: Re: [PATCH v4] drivers/block/mtip32xx: Adding new driver mtip32xx

On 2011-09-30 07:33, Christoph Hellwig wrote:
> On Fri, Sep 09, 2011 at 10:58:01AM +0200, Jens Axboe wrote:
>>>  - handling of REQ_FUA / REQ_FLUSH requests is completely broken.
>>>    There is a weird barrier flag to mtip_hw_submit_io which set the
>>>    hwardware FUA bit if the FLUSH bit is set on a request.
>>>    Please take a look at how this should be handled, the
>>>    Documentation/block/writeback_cache_control.txt file is the canonical
>>>    resource.  Implementing your driver at the make_request layer
>>>    unfortunately means you will have to do all the hard work yourself.
>>
>> I noticed both of these flush/fua problems too and have fixed them up.
> 
> I sitll can't find anything doing that in your tree while all kinds of
> other patches are in.  In fact I can't find a place that sends
> ATA_CMD_FLUSH/ATA_CMD_FLUSH_EXT commands, not the required queue
> draining for it.
> 
> And this stuff really makes me nervous - we get a driver for a new,
> expensive high end device and there seems absolutely no concern for
> data integrity, or testing of it.

I'm away from home, so changes have been coming in through the laptop.
But don't worry about the driver, it's sort-of in a staging position at
the moment. Before Micron has resolved the issues around queueing etc,
it's not going to be merged into mainline.

> Or does the device not even have a volatile cache at all, and we could
> just remove the FUA code?  In this case it should be clearly documented
> in the driver.

See reply from Micron folks, there's no write back cache currently.

-- 
Jens Axboe

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