From: Arnd Bergmann <arnd@kernel.org>
To: Michael Schmitz <schmitzmic@gmail.com>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>,
scsi <linux-scsi@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Arnd Bergmann <arnd@arndb.de>, Jakub Kicinski <kuba@kernel.org>,
Christoph Hellwig <hch@infradead.org>,
Marek Szyprowski <m.szyprowski@samsung.com>,
Robin Murphy <robin.murphy@arm.com>,
Linux IOMMU <iommu@lists.linux-foundation.org>,
Khalid Aziz <khalid@gonehiking.org>,
"Maciej W . Rozycki" <macro@orcam.me.uk>,
Matt Wang <wwentao@vmware.com>,
Miquel van Smoorenburg <mikevs@xs4all.net>,
Mark Salyzyn <salyzyn@android.com>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Linux-Arch <linux-arch@vger.kernel.org>,
alpha <linux-alpha@vger.kernel.org>,
linux-m68k <linux-m68k@lists.linux-m68k.org>,
Parisc List <linux-parisc@vger.kernel.org>,
Denis Efremov <efremov@linux.com>,
Michael Ellerman <mpe@ellerman.id.au>
Subject: Re: [PATCH v2 3/3] arch/*/: remove CONFIG_VIRT_TO_BUS
Date: Tue, 28 Jun 2022 09:08:14 +0200 [thread overview]
Message-ID: <CAK8P3a1ivqYB38c_QTjG8e85ZBnCB6HEa-6LR1HDc8shG1Pwmw@mail.gmail.com> (raw)
In-Reply-To: <9289fd82-285c-035f-5355-4d70ce4f87b0@gmail.com>
On Tue, Jun 28, 2022 at 5:25 AM Michael Schmitz <schmitzmic@gmail.com> wrote:
> Am 28.06.2022 um 09:12 schrieb Michael Schmitz:
>
> Leaving the bounce buffer handling in place, and taking a few other
> liberties - this is what converting the easiest case (a3000 SCSI) might
> look like. Any obvious mistakes? The mvme147 driver would be very
> similar to handle (after conversion to a platform device).
>
> The driver allocates bounce buffers using kmalloc if it hits an
> unaligned data buffer - can such buffers still even happen these days?
> If I understand dma_map_single() correctly, the resulting dma handle
> would be equally misaligned?
>
> To allocate a bounce buffer, would it be OK to use dma_alloc_coherent()
> even though AFAIU memory used for DMA buffers generally isn't consistent
> on m68k?
I think it makes sense to skip the bounce buffering as you do here:
the only standardized way we have for integrating that part is to
use the swiotlb infrastructure, but as you mentioned earlier that
part is probably too resource-heavy here for Amiga.
I see two other problems with your patch though:
a) you still duplicate the cache handling: the cache_clear()/cache_push()
is supposed to already be done by dma_map_single() when the device
is not cache-coherent.
b) The bounce buffer is never mapped here, instead you have the
virt_to_phys() here, which is not the same. I think you need to map
the pointer that actually gets passed down to the device after deciding
to use a bouce buffer or not.
Arnd
next prev parent reply other threads:[~2022-06-28 7:08 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 [this message]
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
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