linux-kernel - Re: [PATCH V3 1/1] ST SPEAr: PCIE gadget suppport

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Message-ID: <4D54E39C.6070306@st.com>
Date:	Fri, 11 Feb 2011 12:52:04 +0530
From:	pratyush <pratyush.anand@...com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, Greg KH <gregkh@...e.de>,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [PATCH V3 1/1] ST SPEAr: PCIE gadget suppport

On 2/11/2011 2:22 AM, Andrew Morton wrote:
> On Thu, 10 Feb 2011 15:19:53 +0530
> pratyush <pratyush.anand@...com> wrote:
> 
>> On 2/10/2011 4:59 AM, Andrew Morton wrote:
>>> On Thu, 3 Feb 2011 19:39:09 +0530
>>> Pratyush Anand <pratyush.anand@...com> wrote:
>>>
>>>> This is a configurable gadget. can be configured by configfs interface. Any
>>>> IP available at PCIE bus can be programmed to be used by host
>>>> controller.It supoorts both INTX and MSI.
>>>> By default, gadget is configured for INTX and SYSRAM1 is mapped to BAR0
>>>> with size 0x1000
>>>>
>>>>
>>>> ...
>>>>
>>>> --- /dev/null
>>>> +++ b/Documentation/ABI/testing/configfs-spear-pcie-gadget
>>>> @@ -0,0 +1,30 @@
>>>> +What:		/config/pcie-gadget
>>>> +Date:		Feb 2011
>>>> +KernelVersion:	2.6.37
>>>> +Contact:	Pratyush Anand <pratyush.anand@...com>
>>>> +Description:
>>>> +
>>>> +	Interface is used to configure selected dual mode pcie controller
>>>> +	as device and then program its various registers to configure it
>>>> +	as a particular device type.
>>>> +	This interfaces can be used to show spear's pcie device capability.
>>>> +
>>>> +	Nodes are only visible when configfs is mounted. To mount configfs
>>>> +	in /config directory use:
>>>> +	# mount -t configfs none /config/
>>>> +
>>>> +	/config/pcie-gadget/
>>>> +		link ... used to enable ltssm and read its status.
>>>> +		int_type ...used to configure and read type of supported
>>>> +			interrupt
>>>> +		no_of_msi ... used to configure number of MSI vector needed and
>>>> +			to read no of MSI granted.
>>>> +		inta ... write 1 to assert INTA and 0 to de-assert.
>>>> +		send_msi ... write MSI vector to be sent.
>>>> +		vendor_id ... used to write and read vendor id (hex)
>>>> +		device_id ... used to write and read device id (hex)
>>>> +		bar0_size ... used to write and read bar0_size
>>>> +		bar0_address ... used to write and read bar0 mapped area in hex.
>>>> +		bar0_rw_offset ... used to write and read offset of bar0 where
>>>> +			bar0_data will be written or read.
>>>> +		bar0_data ... used to write and read data at bar0_rw_offset.
>>>
>>> This interface implies that there will only ever be one device in the
>>> machine, yes?  Seems a bit short-sighted?
>>>
>>
>> This device supports only one BAR in EP mode.
> 
> I don't understand that.
> 
> What happens if someone builds a computer with three of these devices
> in it?
> 

I understood it. I will modify the code to work with multiple instances of
pcie device.

>>>> +		flags &= ~PCI_MSI_FLAGS_QMASK;
>>>> +		flags |= vec << 1;
>>>> +		spear_dbi_write_reg(config, cap + PCI_MSI_FLAGS, 1, flags);
>>>> +	} else
>>>> +		return -EINVAL;
>>>> +
>>>> +	strcpy(config->int_type, int_type);
>>>> +
>>>> +	return count;
>>>> +}
>>>> +
>>>> +static ssize_t pcie_gadget_show_no_of_msi(
>>>> +		struct spear_pcie_gadget_config *config,
>>>> +		char *buf)
>>>> +{
>>>> +	struct pcie_app_reg __iomem *app_reg =
>>>> +		(struct pcie_app_reg __iomem *)config->va_app_base;
>>>> +	u32 cap, vector, vec, flags;
>>>> +
>>>> +	if ((readl(&app_reg->msg_status) & (1 << CFG_MSI_EN_ID))
>>>> +			!= (1 << CFG_MSI_EN_ID))
>>>> +		vector = 0;
>>>> +	else {
>>>> +		cap = pci_find_own_capability(config, PCI_CAP_ID_MSI);
>>>> +		spear_dbi_read_reg(config, cap + PCI_MSI_FLAGS, 1, &flags);
>>>> +		flags &= ~PCI_MSI_FLAGS_QSIZE;
>>>> +		vec = flags >> 4;
>>>> +		vector = 1;
>>>> +		while (vec--)
>>>> +			vector *= 2;
>>>> +	}
>>>> +	config->configured_msi = vector;
>>>
>>> Wait.  A "show" function is modifying kernel state?!?!?
>>>
>>
>> this show is a must call part of MSI vector negotiation.
>> A device must read first configured number of MSI, before 
>> sending any MSI. Here value of vector is read from HW
>> and stored in a SW variable. So, it is not programmed
>> by any application input.
> 
> What happens if a (buggy?) application tries to send an MSI before
> calling pcie_gadget_show_no_of_msi()?
> 

It will receive an -EINVAL.

Regards
Pratyush

> 
> .
> 

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