From: Arnd Bergmann <arnd@arndb.de>
To: Xianting TIan <xianting.tian@linux.alibaba.com>
Cc: Arnd Bergmann <arnd@arndb.de>,
gregkh <gregkh@linuxfoundation.org>,
Jiri Slaby <jirislaby@kernel.org>, Amit Shah <amit@kernel.org>,
Omar Sandoval <osandov@fb.com>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
"open list:DRM DRIVER FOR QEMU'S CIRRUS DEVICE"
<virtualization@lists.linux-foundation.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Guo Ren <guoren@kernel.org>
Subject: Re: [PATCH v4 1/2] tty: hvc: pass DMA capable memory to put_chars()
Date: Thu, 12 Aug 2021 10:54:22 +0200 [thread overview]
Message-ID: <CAK8P3a2ykLvJkhX+wDAOHdyLHjPFAfhOxi5BNM9kTKv_8F7VQg@mail.gmail.com> (raw)
In-Reply-To: <f18d017b-d6f7-cf87-8859-8d6b50c7c289@linux.alibaba.com>
On Thu, Aug 12, 2021 at 10:08 AM Xianting TIan
<xianting.tian@linux.alibaba.com> wrote:
> 在 2021/8/6 下午10:51, Arnd Bergmann 写道:
> > On Fri, Aug 6, 2021 at 5:01 AM Xianting Tian
> >> +#define __ALIGNED__ __attribute__((__aligned__(sizeof(long))))
> > I think you need a higher alignment for DMA buffers, instead of sizeof(long),
> > I would suggest ARCH_DMA_MINALIGN.
>
> As some ARCH(eg, x86, riscv) doesn't define ARCH_DMA_MINALIG, so i think
> it 's better remain the code unchanged,
>
> I will send v5 patch soon.
I think you could just use "L1_CACHE_BYTES" as the alignment in this case.
This will make the structure slightly larger for architectures that do not have
alignment constraints on DMA buffers, but using a smaller alignment is
clearly wrong. Another option would be to use ARCH_KMALLOC_MINALIGN.
Note that there is a patch to add ARCH_DMA_MINALIGN to riscv already,
as some implementations do not have coherent DMA. I had failed to
realized though that on x86 you do not get an ARCH_DMA_MINALIGN
definition.
Arnd
next prev parent reply other threads:[~2021-08-12 8:54 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-06 3:01 [PATCH v4 0/2] make hvc pass dma capable memory to its backend Xianting Tian
2021-08-06 3:01 ` [PATCH v4 1/2] tty: hvc: pass DMA capable memory to put_chars() Xianting Tian
2021-08-06 14:51 ` Arnd Bergmann
2021-08-07 15:00 ` Xianting Tian
2021-08-12 8:07 ` Xianting TIan
2021-08-12 8:54 ` Arnd Bergmann [this message]
2021-08-12 9:14 ` Xianting TIan
2021-08-06 3:01 ` [PATCH v4 2/2] virtio-console: remove unnecessary kmemdup() Xianting Tian
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