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From: Sinan Kaya <>
To: James Bottomley <>,,,,
	Helge Deller <>,
	Philippe Ombredanne <>,
	Kate Stewart <>,
	Thomas Gleixner <>,
	Greg Kroah-Hartman <>,
Subject: Re: [PATCH v2 2/2] parisc: define stronger ordering for the default readX()
Date: Tue, 17 Apr 2018 10:13:28 -0400	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

Hi James,

> Perhaps if you gave an example of the actual problem you're trying to
> fix we could assess if it affects parisc.

Let me clarify myself here. Maybe, there is a better solution.

		/* assign ownership */
		desc->status = DEVICE_OWN;

		/* notify device of new descriptors */
		writel(DESC_NOTIFY, doorbell);

The difference between writel() and writel_relax() is writel() guarantees
memory transactions to be flushed to the device before the register write.
writel_relaxed() does not provide any guarantees about the memory and IO

Similarly, readl() provides following code to observe the DMA result while
readl_relaxed() does not provide this guarantee.

Ideally, you want to embed rmb() and wmb() into the writel() and readl()
to provide this guarantee.

PA-RISC doesn't seem to support neither one of the barrier types. If you are
familiar with the architecture, maybe you could guide us here.

Is __raw_writeX() enough to provide this guarantee for this architecture?


Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.

  reply	other threads:[~2018-04-17 14:13 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-17  4:08 [PATCH v2 1/2] parisc: define stronger ordering for the default writeX() Sinan Kaya
2018-04-17  4:08 ` [PATCH v2 2/2] parisc: define stronger ordering for the default readX() Sinan Kaya
2018-04-17  9:37   ` James Bottomley
2018-04-17 14:13     ` Sinan Kaya [this message]
2018-04-17 15:55       ` James Bottomley
2018-04-17 18:28         ` Sinan Kaya
2018-04-17 22:53           ` John David Anglin
2018-04-18 13:39             ` Sinan Kaya

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