From: Michael Schmitz <schmitzmic@gmail.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>,
Linux-Arch <linux-arch@vger.kernel.org>,
scsi <linux-scsi@vger.kernel.org>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Jakub Kicinski <kuba@kernel.org>, Arnd Bergmann <arnd@arndb.de>,
Miquel van Smoorenburg <mikevs@xs4all.net>,
Denis Efremov <efremov@linux.com>,
linux-m68k <linux-m68k@lists.linux-m68k.org>,
John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
Khalid Aziz <khalid@gonehiking.org>,
Arnd Bergmann <arnd@kernel.org>,
Parisc List <linux-parisc@vger.kernel.org>,
Robin Murphy <robin.murphy@arm.com>,
Matt Wang <wwentao@vmware.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Mark Salyzyn <salyzyn@android.com>,
Linux IOMMU <iommu@lists.linux-foundation.org>,
alpha <linux-alpha@vger.kernel.org>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
"Maciej W . Rozycki" <macro@orcam.me.uk>
Subject: Re: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO_BUS
Date: Fri, 1 Jul 2022 07:26:05 +1200 [thread overview]
Message-ID: <13e45965-4e55-11b1-bfdc-59efaad27464@gmail.com> (raw)
In-Reply-To: <YrvwZi9NQSpFjStX@infradead.org>
Hi Christoph,
On 29/06/22 18:25, Christoph Hellwig wrote:
> On Wed, Jun 29, 2022 at 09:38:00AM +1200, Michael Schmitz wrote:
>> That's one of the 'liberties' I alluded to. The reason I left these in is
>> that I'm none too certain what device feature the DMA API uses to decide a
>> device isn't cache-coherent.
> The DMA API does not look at device features at all. It needs to be
> told so by the platform code. Once an architecture implements the
> hooks to support non-coherent DMA all devices are treated as
> non-coherent by default unless overriden by the architecture either
> globally (using the global dma_default_coherent variable) or per-device
> (using the dev->dma_coherent field, usually set by arch_setup_dma_ops).
Haven't got any of that, so non-coherent DMA is all we can use (even
though some of the RAM used for bounce buffers may actually be coherent
due to the page table cache bits).
>
>> If it's dev->coherent_dma_mask, the way I set
>> up the device in the a3000 driver should leave the coherent mask unchanged.
>> For the Zorro drivers, devices are set up to use the same storage to store
>> normal and coherent masks - something we most likely want to change. I need
>> to think about the ramifications of that.
> No, the coherent mask is slightly misnamed amd not actually related.
Thanks, that had me confused.
Cheers,
Michael
prev parent reply other threads:[~2022-06-30 19:26 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-17 12:57 [PATCH v2 0/3] phase out CONFIG_VIRT_TO_BUS Arnd Bergmann
2022-06-17 12:57 ` [PATCH v2 1/3] scsi: dpt_i2o: drop stale VIRT_TO_BUS dependency Arnd Bergmann
2022-06-21 8:43 ` Hannes Reinecke
2022-06-17 12:57 ` [PATCH v2 2/3] scsi: BusLogic remove bus_to_virt Arnd Bergmann
2022-06-17 14:02 ` Robin Murphy
2022-06-21 8:45 ` Hannes Reinecke
2022-06-21 21:56 ` Khalid Aziz
2022-06-23 14:47 ` Arnd Bergmann
2022-06-24 15:38 ` Khalid Aziz
2022-06-24 15:43 ` Arnd Bergmann
2022-06-17 12:57 ` [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO_BUS Arnd Bergmann
2022-06-18 1:06 ` Michael Schmitz
2022-06-24 9:10 ` Arnd Bergmann
2022-06-26 5:21 ` Michael Schmitz
2022-06-26 8:36 ` Arnd Bergmann
2022-06-27 8:09 ` Michael Schmitz
2022-06-27 8:26 ` Geert Uytterhoeven
2022-06-27 21:12 ` Michael Schmitz
2022-06-28 3:25 ` Michael Schmitz
2022-06-28 7:03 ` Geert Uytterhoeven
2022-06-28 21:03 ` Michael Schmitz
2022-06-28 21:50 ` Arnd Bergmann
2022-06-28 23:09 ` Michael Schmitz
2022-06-28 23:50 ` Bart Van Assche
2022-06-29 0:01 ` Michael Schmitz
2022-06-29 0:14 ` Michael Schmitz
2022-06-29 6:21 ` Christoph Hellwig
2022-06-30 19:21 ` Michael Schmitz
2022-06-30 8:04 ` David Laight
2022-06-30 9:40 ` Christophe Leroy
2022-06-30 10:32 ` David Laight
2022-06-28 7:08 ` Arnd Bergmann
2022-06-28 21:38 ` Michael Schmitz
2022-06-28 21:55 ` Arnd Bergmann
2022-06-28 23:43 ` Michael Schmitz
2022-06-29 6:25 ` Christoph Hellwig
2022-06-30 19:26 ` Michael Schmitz [this message]
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