linux-kernel - Re: [PATCH 19/34] AMD IOMMU: add functions to send IOMMU commands

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Message-Id: <20080709190453.527535f7.akpm@linux-foundation.org>
Date:	Wed, 9 Jul 2008 19:04:53 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Joerg Roedel <joerg.roedel@....com>
Cc:	tglx@...utronix.de, mingo@...hat.com, linux-kernel@...r.kernel.org,
	iommu@...ts.linux-foundation.org, bhavna.sarathy@....com,
	Sebastian.Biemueller@....com, robert.richter@....com,
	joro@...tes.org
Subject: Re: [PATCH 19/34] AMD IOMMU: add functions to send IOMMU commands

On Thu, 26 Jun 2008 21:27:55 +0200 Joerg Roedel <joerg.roedel@....com> wrote:

> This patch adds generic handling function as well as all functions to send
> specific commands to the IOMMU hardware as required by this driver.
> 
> Signed-off-by: Joerg Roedel <joerg.roedel@....com>
> ---
>  arch/x86/kernel/amd_iommu.c |  106 +++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 106 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/x86/kernel/amd_iommu.c b/arch/x86/kernel/amd_iommu.c
> index 90392c7..a24ee4a 100644
> --- a/arch/x86/kernel/amd_iommu.c
> +++ b/arch/x86/kernel/amd_iommu.c
> @@ -37,4 +37,110 @@ struct command {
>  	u32 data[4];
>  };
>  
> +static int __iommu_queue_command(struct amd_iommu *iommu, struct command *cmd)
> +{
> +	u32 tail, head;
> +	u8 *target;
> +
> +	tail = readl(iommu->mmio_base + MMIO_CMD_TAIL_OFFSET);
> +	target = (iommu->cmd_buf + tail);
> +	memcpy_toio(target, cmd, sizeof(*cmd));
> +	tail = (tail + sizeof(*cmd)) % iommu->cmd_buf_size;
> +	head = readl(iommu->mmio_base + MMIO_CMD_HEAD_OFFSET);
> +	if (tail == head)
> +		return -ENOMEM;
> +	writel(tail, iommu->mmio_base + MMIO_CMD_TAIL_OFFSET);
> +
> +	return 0;
> +}
> +
> +static int iommu_queue_command(struct amd_iommu *iommu, struct command *cmd)
> +{
> +	unsigned long flags;
> +	int ret;
> +
> +	spin_lock_irqsave(&iommu->lock, flags);
> +	ret = __iommu_queue_command(iommu, cmd);
> +	spin_unlock_irqrestore(&iommu->lock, flags);
> +
> +	return ret;
> +}
> +
> +static int iommu_completion_wait(struct amd_iommu *iommu)
> +{
> +	int ret;
> +	struct command cmd;
> +	volatile u64 ready = 0;
> +	unsigned long ready_phys = virt_to_phys(&ready);
> +
> +	memset(&cmd, 0, sizeof(cmd));
> +	cmd.data[0] = LOW_U32(ready_phys) | CMD_COMPL_WAIT_STORE_MASK;
> +	cmd.data[1] = HIGH_U32(ready_phys);
> +	cmd.data[2] = 1; /* value written to 'ready' */
> +	CMD_SET_TYPE(&cmd, CMD_COMPL_WAIT);
> +
> +	iommu->need_sync = 0;
> +
> +	ret = iommu_queue_command(iommu, &cmd);
> +
> +	if (ret)
> +		return ret;
> +
> +	while (!ready)
> +		cpu_relax();

I busywait is a big red flag.  An uncommented one is not acceptable IMO.

What is the maximum duration?

Is it not possible to sleep and await an interrupt?

Should we implement a timeout in case the hardware is busted?

> +	return 0;
> +}
> +
> +static int iommu_queue_inv_dev_entry(struct amd_iommu *iommu, u16 devid)
> +{
> +	struct command cmd;

`command' was a poorly-chosen identifier for this structure.  Too generic.

> +	BUG_ON(iommu == NULL);
> +
> +	memset(&cmd, 0, sizeof(cmd));
> +	CMD_SET_TYPE(&cmd, CMD_INV_DEV_ENTRY);
> +	cmd.data[0] = devid;
> +
> +	iommu->need_sync = 1;
> +
> +	return iommu_queue_command(iommu, &cmd);
> +}
> +
> +static int iommu_queue_inv_iommu_pages(struct amd_iommu *iommu,
> +		u64 address, u16 domid, int pde, int s)
> +{
> +	struct command cmd;
> +
> +	memset(&cmd, 0, sizeof(cmd));
> +	address &= PAGE_MASK;
> +	CMD_SET_TYPE(&cmd, CMD_INV_IOMMU_PAGES);
> +	cmd.data[1] |= domid;
> +	cmd.data[2] = LOW_U32(address);
> +	cmd.data[3] = HIGH_U32(address);
> +	if (s)
> +		cmd.data[2] |= CMD_INV_IOMMU_PAGES_SIZE_MASK;
> +	if (pde)
> +		cmd.data[2] |= CMD_INV_IOMMU_PAGES_PDE_MASK;
> +
> +	iommu->need_sync = 1;
> +
> +	return iommu_queue_command(iommu, &cmd);
> +}
> +
> +static int iommu_flush_pages(struct amd_iommu *iommu, u16 domid,
> +		u64 address, size_t size)
> +{
> +	int i;
> +	unsigned pages = to_pages(address, size);
> +
> +	address &= PAGE_MASK;
> +
> +	for (i = 0; i < pages; ++i) {
> +		iommu_queue_inv_iommu_pages(iommu, address, domid, 0, 0);
> +		address += PAGE_SIZE;
> +	}
> +
> +	return 0;
> +}

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