From: Nikita Yushchenko <nikita.yoush@cogentembedded.com>
To: Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Artemi Ivanov <artemi.ivanov@cogentembedded.com>
Subject: blk_queue_bounce_limit() broken for mask=0xffffffff on 64bit archs
Date: Mon, 9 Jan 2017 23:48:11 +0300 [thread overview]
Message-ID: <632ad7f3-e837-a17c-5ba7-ed9800ba3ec0@cogentembedded.com> (raw)
Hi
There is a use cases when architecture is 64-bit but hardware supports
only DMA to lower 4G of address space. E.g. NVMe device on RCar PCIe host.
For such cases, it looks proper to call blk_queue_bounce_limit() with
mask set to 0xffffffff - thus making block layer to use bounce buffers
for any addresses beyond 4G. To support that, architecture provides
GFP_DMA zone that covers exactly low 4G on arm64.
However setting this limit does not work:
if (b_pfn < (min_t(u64, 0xffffffffUL, BLK_BOUNCE_HIGH) >> PAGE_SHIFT))
dma = 1;
When mask is 0xffffffff that condition is false
q->limits.bounce_pfn = max(max_low_pfn, b_pfn);
this line is executed and replaces any limit with end of memory (on
64bit arch all memory is low).
Not sure how to fix this properly. Any hints?
next reply other threads:[~2017-01-09 20:48 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-09 20:48 Nikita Yushchenko [this message]
2017-01-09 20:59 ` blk_queue_bounce_limit() broken for mask=0xffffffff on 64bit archs Christoph Hellwig
2017-01-13 6:07 ` Ming Lei
2017-01-13 6:10 ` Nikita Yushchenko
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