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From: Christoph Hellwig <hch@infradead.org>
To: Peter Geis <pgwipeout@gmail.com>
Cc: Shawn Lin <shawn.lin@rock-chips.com>,
	Simon Xue <xxm@rock-chips.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	linux-pci@vger.kernel.org,
	"open list:ARM/Rockchip SoC..."
	<linux-rockchip@lists.infradead.org>,
	devicetree@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
	Johan Jonker <jbx6244@gmail.com>,
	Heiko Stuebner <heiko@sntech.de>
Subject: Re: [PATCH v7] PCI: rockchip: Add Rockchip RK356X host controller driver
Date: Thu, 29 Apr 2021 07:41:17 +0100	[thread overview]
Message-ID: <20210429064117.GA2214470@infradead.org> (raw)
In-Reply-To: <CAMdYzYr=i7X22-38VyY-GQLWs+aV+ZcWwO_uDymFxmaNO8SpmA@mail.gmail.com>

On Wed, Apr 28, 2021 at 09:42:37PM -0400, Peter Geis wrote:
> I have functional MSI support, some devices do not support MSIs
> however and need legacy INTx.
> I'd like to point out that the downstream patch does not actually work
> on downstream.
> The GFP_DMA32 flag is discarded by the slab allocator, this breaks MSI
> allocation when the PCIe driver probes.
> I hacked together my own version which works but would definitely not
> be accepted for submission.

Seriously folks.  Never, ever use GFP_DMA or GFP_DMA32 in actual driver
code.  They fundamentally don't do what you want.  Devices as a rule of
thumb do care about DMA addressability, not CPU addressability, so they
must use the DMA API to allocate the memory, and the dma mask to control
addressability.

WARNING: multiple messages have this Message-ID (diff)
From: Christoph Hellwig <hch@infradead.org>
To: Peter Geis <pgwipeout@gmail.com>
Cc: Shawn Lin <shawn.lin@rock-chips.com>,
	Simon Xue <xxm@rock-chips.com>,
	Bjorn Helgaas <bhelgaas@google.com>,
	Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
	linux-pci@vger.kernel.org,
	"open list:ARM/Rockchip SoC..."
	<linux-rockchip@lists.infradead.org>,
	devicetree@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
	Johan Jonker <jbx6244@gmail.com>,
	Heiko Stuebner <heiko@sntech.de>
Subject: Re: [PATCH v7] PCI: rockchip: Add Rockchip RK356X host controller driver
Date: Thu, 29 Apr 2021 07:41:17 +0100	[thread overview]
Message-ID: <20210429064117.GA2214470@infradead.org> (raw)
In-Reply-To: <CAMdYzYr=i7X22-38VyY-GQLWs+aV+ZcWwO_uDymFxmaNO8SpmA@mail.gmail.com>

On Wed, Apr 28, 2021 at 09:42:37PM -0400, Peter Geis wrote:
> I have functional MSI support, some devices do not support MSIs
> however and need legacy INTx.
> I'd like to point out that the downstream patch does not actually work
> on downstream.
> The GFP_DMA32 flag is discarded by the slab allocator, this breaks MSI
> allocation when the PCIe driver probes.
> I hacked together my own version which works but would definitely not
> be accepted for submission.

Seriously folks.  Never, ever use GFP_DMA or GFP_DMA32 in actual driver
code.  They fundamentally don't do what you want.  Devices as a rule of
thumb do care about DMA addressability, not CPU addressability, so they
must use the DMA API to allocate the memory, and the dma mask to control
addressability.

_______________________________________________
Linux-rockchip mailing list
Linux-rockchip@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-rockchip

  parent reply	other threads:[~2021-04-29  6:41 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-14  7:03 [PATCH v7] PCI: rockchip: Add Rockchip RK356X host controller driver Simon Xue
2021-04-14  7:03 ` Simon Xue
2021-04-28 16:20 ` Peter Geis
2021-04-28 16:20   ` Peter Geis
2021-04-29  0:46   ` Shawn Lin
2021-04-29  1:42     ` Peter Geis
2021-04-29  1:42       ` Peter Geis
2021-04-29  6:32       ` Shawn Lin
2021-04-29 11:21         ` Peter Geis
2021-04-29 11:21           ` Peter Geis
2021-04-29  6:41       ` Christoph Hellwig [this message]
2021-04-29  6:41         ` Christoph Hellwig
     [not found]         ` <CAMdYzYrbfD-jFC3uPVPkhjXWZGeaUw5X=0w1Q=m-6OuhEGOKkQ@mail.gmail.com>
     [not found]           ` <20210429115451.GA2287423@infradead.org>
2021-04-29 12:16             ` Peter Geis
2021-04-29 12:16               ` Peter Geis

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