From: Timur Tabi <timur@codeaurora•org>
To: Arnd Bergmann <arnd@arndb•de>
Cc: netdev@vger•kernel.org, devicetree@vger•kernel.org,
linux-arm-msm@vger•kernel.org, sdharia@codeaurora•org,
shankerd@codeaurora•org, vikrams@codeaurora•org,
cov@codeaurora•org, gavidov@codeaurora•org, robh+dt@kernel•org,
andrew@lunn•ch, bjorn.andersson@linaro•org, mlangsdo@redhat•com,
jcm@redhat•com, agross@codeaurora•org, davem@davemloft•net,
f.fainelli@gmail•com, catalin.marinas@arm•com
Subject: Re: [PATCH] [v6] net: emac: emac gigabit ethernet controller driver
Date: Thu, 4 Aug 2016 09:24:54 -0500 [thread overview]
Message-ID: <57A35036.2030604@codeaurora.org> (raw)
In-Reply-To: <3036653.SbY9jG7XMU@wuerfel>
Arnd Bergmann wrote:
> This is basically ok, but then I think you should pass GFP_DMA
> or GFP_DMA32 to all allocations that the driver does after
> the 64-bit mask fails, otherwise you get a significant overhead
> in the bounce buffers.
Well, for starters, ZONE_DMA32 is the same as ZONE_NORMAL on ARM,
because CONFIG_ZONE_DMA32 is not defined.
#ifdef CONFIG_ZONE_DMA32
#define OPT_ZONE_DMA32 ZONE_DMA32
#else
#define OPT_ZONE_DMA32 ZONE_NORMAL
#endif
(I wonder if this should say instead:
#ifdef CONFIG_ZONE_DMA32
#define OPT_ZONE_DMA32 ZONE_DMA32
#else
#define OPT_ZONE_DMA32 ZONE_DMA <----
#endif
)
However, I'm not sure where I should be using GFP_DMA anyway. Whenever
the driver allocates memory for DMA, it uses dma_zalloc_coherent():
ring_header->v_addr = dma_zalloc_coherent(dev, ring_header->size,
&ring_header->dma_addr,
GFP_KERNEL);
and I don't think I need to pass GFP_DMA to dma_zalloc_coherent. Every
other memory allocation is a kmalloc variant, but that's never for DMA,
so that memory can be anywhere.
I found about 70 drivers that fall-back to 32-bit DMA if 64-bit fails.
None of them do as you suggest. They all just set the mask to 64 or 32
and that's it.
Some drivers set NETIF_F_HIGHDMA if 64-bit DMA is enabled:
if (pci_using_dac)
netdev->features |= NETIF_F_HIGHDMA;
I could do this, but I think it has no meaning on ARM64 because it
depends on CONFIG_HIGHMEM.
--
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm
Technologies, Inc. Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.
next prev parent reply other threads:[~2016-08-04 14:24 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-24 23:46 [PATCH] [v6] net: emac: emac gigabit ethernet controller driver Timur Tabi
2016-06-28 20:56 ` Rob Herring
2016-06-29 7:55 ` David Miller
2016-06-29 8:17 ` Arnd Bergmann
2016-06-29 12:17 ` Timur Tabi
2016-06-29 14:07 ` Arnd Bergmann
2016-06-29 14:33 ` Timur Tabi
2016-06-29 15:04 ` Arnd Bergmann
2016-06-29 15:10 ` Timur Tabi
2016-06-29 15:34 ` Arnd Bergmann
2016-06-29 15:46 ` Timur Tabi
2016-06-29 19:45 ` Arnd Bergmann
2016-06-29 20:16 ` Timur Tabi
2016-07-01 13:54 ` Arnd Bergmann
2016-08-03 21:24 ` Timur Tabi
2016-08-04 9:21 ` Arnd Bergmann
2016-08-04 14:24 ` Timur Tabi [this message]
2016-07-03 23:04 ` Lino Sanfilippo
2016-07-28 19:12 ` Timur Tabi
2016-07-30 10:26 ` Lino Sanfilippo
2016-08-02 17:59 ` Timur Tabi
2016-08-03 20:00 ` Timur Tabi
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