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SubjectRe: [PATCH V2 2/2] mailbox: introduce ARM SMC based mailbox
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On 6/3/19 1:30 AM, peng.fan@nxp.com wrote:
> From: Peng Fan <peng.fan@nxp.com>
>
> This mailbox driver implements a mailbox which signals transmitted data
> via an ARM smc (secure monitor call) instruction. The mailbox receiver
> is implemented in firmware and can synchronously return data when it
> returns execution to the non-secure world again.
> An asynchronous receive path is not implemented.
> This allows the usage of a mailbox to trigger firmware actions on SoCs
> which either don't have a separate management processor or on which such
> a core is not available. A user of this mailbox could be the SCP
> interface.
>
> Modified from Andre Przywara's v2 patch
> https://lore.kernel.org/patchwork/patch/812999/
>
> Cc: Andre Przywara <andre.przywara@arm.com>
> Signed-off-by: Peng Fan <peng.fan@nxp.com>
> ---

[snip]

+#define ARM_SMC_MBOX_USB_IRQ BIT(1)

That flag appears unused.

> +static int arm_smc_mbox_probe(struct platform_device *pdev)
> +{
> + struct device *dev = &pdev->dev;
> + struct mbox_controller *mbox;
> + struct arm_smc_chan_data *chan_data;
> + const char *method;
> + bool use_hvc = false;
> + int ret, irq_count, i;
> + u32 val;
> +
> + if (!of_property_read_u32(dev->of_node, "arm,num-chans", &val)) {
> + if (val < 1 || val > INT_MAX) {
> + dev_err(dev, "invalid arm,num-chans value %u of %pOFn\n", val, pdev->dev.of_node);
> + return -EINVAL;
> + }
> + }

Should not the upper bound check be done against UINT_MAX since val is
an unsigned int?

> +
> + irq_count = platform_irq_count(pdev);
> + if (irq_count == -EPROBE_DEFER)
> + return irq_count;
> +
> + if (irq_count && irq_count != val) {
> + dev_err(dev, "Interrupts not match num-chans\n");

Interrupts property does not match \"arm,num-chans\" would be more correct.

> + return -EINVAL;
> + }
> +
> + if (!of_property_read_string(dev->of_node, "method", &method)) {
> + if (!strcmp("hvc", method)) {
> + use_hvc = true;
> + } else if (!strcmp("smc", method)) {
> + use_hvc = false;
> + } else {
> + dev_warn(dev, "invalid \"method\" property: %s\n",
> + method);
> +
> + return -EINVAL;
> + }

Having at least one method specified does not seem to be checked later
on in the code, so if I omitted to specify that property, we would still
register the mailbox and default to use "smc" since the
ARM_SMC_MBOX_USE_HVC flag would not be set, would not we want to make
sure that we do have in fact a valid method specified given the binding
documents that property as mandatory?

[snip]

> + mbox->txdone_poll = false;
> + mbox->txdone_irq = false;
> + mbox->ops = &arm_smc_mbox_chan_ops;
> + mbox->dev = dev;
> +
> + ret = mbox_controller_register(mbox);
> + if (ret)
> + return ret;
> +
> + platform_set_drvdata(pdev, mbox);

I would move this above mbox_controller_register() that way there is no
room for race conditions in case another part of the driver expects to
have pdev->dev.drvdata set before the mbox controller is registered.
Since you use devm_* functions for everything, you may even remove that
call.

[snip]

> +#ifndef _LINUX_ARM_SMC_MAILBOX_H_
> +#define _LINUX_ARM_SMC_MAILBOX_H_
> +
> +struct arm_smccc_mbox_cmd {
> + unsigned long a0, a1, a2, a3, a4, a5, a6, a7;
> +};

Do you expect this to be used by other in-kernel users? If so, it might
be good to document how a0 can have a special meaning and be used as a
substitute for the function_id?
--
Florian

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