From: Christoph Hellwig <hch@lst.de>
To: Alexey Kardashevskiy <aik@ozlabs.ru>
Cc: "Oliver O'Halloran" <oohall@gmail.com>,
linuxppc-dev@lists.ozlabs.org, "Christoph Hellwig" <hch@lst.de>,
"Cédric Le Goater" <clg@kaod.org>
Subject: Re: [PATCH kernel] powerpc/dma: Fix dma_map_ops::get_required_mask
Date: Tue, 8 Sep 2020 07:44:16 +0200 [thread overview]
Message-ID: <20200908054416.GA13585@lst.de> (raw)
In-Reply-To: <20200908015106.79661-1-aik@ozlabs.ru>
On Tue, Sep 08, 2020 at 11:51:06AM +1000, Alexey Kardashevskiy wrote:
> What is dma_get_required_mask() for anyway? What "requires" what here?
Yes, it is a really odd API. It comes from classic old PCI where
64-bit addressing required an additional bus cycle, and various devices
had different addressing schemes, with the smaller addresses beeing
more efficient. So this allows the driver to request the "required"
addressing mode to address all memory. "preferred" might be a better
name as we'll bounce buffer if it isn't met. I also don't really see
why a driver would ever want to use it for a modern PCIe device.
next prev parent reply other threads:[~2020-09-08 5:46 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-08 1:51 [PATCH kernel] powerpc/dma: Fix dma_map_ops::get_required_mask Alexey Kardashevskiy
2020-09-08 5:44 ` Christoph Hellwig [this message]
2020-09-08 12:06 ` Alexey Kardashevskiy
2020-09-08 12:19 ` Christoph Hellwig
[not found] ` <1746dd66810.27bb.1ca38dd7e845b990cd13d431eb58563d@ozlabs.ru>
[not found] ` <20200909075849.GA12282@lst.de>
2020-09-09 9:36 ` Alexey Kardashevskiy
2020-09-15 6:50 ` Christoph Hellwig
2020-09-22 2:26 ` Alexey Kardashevskiy
2020-09-23 14:10 ` Christoph Hellwig
2020-09-24 7:03 ` Alexey Kardashevskiy
2020-09-25 4:56 ` Christoph Hellwig
2021-09-29 8:48 ` Alexey Kardashevskiy
2020-09-08 6:45 ` Michael Ellerman
2020-09-08 11:45 ` Cédric Le Goater
2020-09-10 12:55 ` Michael Ellerman
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