linux-kernel - Re: [RFC][PATCH V4] axi: add AXI bus driver

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Date:	Wed, 13 Apr 2011 22:37:44 +0200
From:	Gábor Stefanik <netrolller.3d@...il.com>
To:	Rafał Miłecki <zajec5@...il.com>
Cc:	Greg KH <greg@...ah.com>, linux-wireless@...r.kernel.org,
	"John W. Linville" <linville@...driver.com>,
	b43-dev@...ts.infradead.org,
	Michael Büsch <mb@...sch.de>,
	Larry Finger <Larry.Finger@...inger.net>,
	George Kashperko <george@...u.edu.ua>,
	Arend van Spriel <arend@...adcom.com>,
	linux-arm-kernel@...ts.infradead.org,
	Russell King <rmk@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	Andy Botting <andy@...ybotting.com>,
	linuxdriverproject <devel@...uxdriverproject.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH V4] axi: add AXI bus driver

On Wed, Apr 13, 2011 at 9:39 PM, Rafał Miłecki <zajec5@...il.com> wrote:
> 2011/4/13 Greg KH <greg@...ah.com>:
>>> diff --git a/drivers/axi/axi_pci_bridge.c b/drivers/axi/axi_pci_bridge.c
>>> new file mode 100644
>>> index 0000000..17e882c
>>> --- /dev/null
>>> +++ b/drivers/axi/axi_pci_bridge.c
>>> @@ -0,0 +1,33 @@
>>> +/*
>>> + * AXI PCI bridge module
>>> + *
>>> + * Licensed under the GNU/GPL. See COPYING for details.
>>> + */
>>> +
>>> +#include "axi_private.h"
>>> +
>>> +#include <linux/axi/axi.h>
>>> +#include <linux/pci.h>
>>> +
>>> +static DEFINE_PCI_DEVICE_TABLE(axi_pci_bridge_tbl) = {
>>> +     { PCI_DEVICE(PCI_VENDOR_ID_BROADCOM, 0x4331) },
>>> +     { PCI_DEVICE(PCI_VENDOR_ID_BROADCOM, 0x4353) },
>>> +     { PCI_DEVICE(PCI_VENDOR_ID_BROADCOM, 0x4727) },
>>> +     { 0, },
>>> +};
>>> +MODULE_DEVICE_TABLE(pci, axi_pci_bridge_tbl);
>>> +
>>> +static struct pci_driver axi_pci_bridge_driver = {
>>> +     .name = "axi-pci-bridge",
>>> +     .id_table = axi_pci_bridge_tbl,
>>> +};
>>> +
>>> +int __init axi_pci_bridge_init(void)
>>> +{
>>> +     return axi_host_pci_register(&axi_pci_bridge_driver);
>>> +}
>>> +
>>> +void __exit axi_pci_bridge_exit(void)
>>> +{
>>> +     axi_host_pci_unregister(&axi_pci_bridge_driver);
>>> +}
>>
>> You register a pci driver that does nothing?  That's not right, you need
>> to then base your axi bus off of that pci device, so it is hooked up
>> correctly in the /sys/devices/ tree.  Otherwise you are somewhere up in
>> the virtual location for your axi bus, right?
>
> Please take a look at:
> driver->probe = axi_host_pci_probe;
> driver->remove = axi_host_pci_remove;
> return pci_register_driver(driver);
>
>
>>> +bool axi_core_is_enabled(struct axi_device *core)
>>> +{
>>> +     if ((axi_aread32(core, AXI_IOCTL) & (AXI_IOCTL_CLK | AXI_IOCTL_FGC))
>>> +         != AXI_IOCTL_CLK)
>>> +             return false;
>>> +     if (axi_aread32(core, AXI_RESET_CTL) & AXI_RESET_CTL_RESET)
>>> +             return false;
>>> +     return true;
>>> +}
>>> +EXPORT_SYMBOL(axi_core_is_enabled);
>>
>> EXPORT_SYMBOL_GPL()?
>>
>> What module uses this?  And why would it care?
>>
>>> +EXPORT_SYMBOL(axi_core_enable);
>>
>> EXPORT_SYMBOL_GPL()?
>>
>> Same goes for your other exports, just want you to be sure here.
>
> Hm, I'm not sure. Using EXPORT_SYMBOL_GPL will forbid closed source
> drivers from using our bus driver, right? I'm don't have preferences
> on this, if you prefer us to force GPL, I can.

Isn't EXPORT_SYMBOL_GPL for symbols that are considered to form a
tight coupling between the kernel and users of the symbol? Using _GPL
just because you are against proprietary drivers in general and want
to force GPL on HW vendors is wrong.

>
>
>>> +u32 xaxi_chipco_gpio_control(struct axi_drv_cc *cc, u32 mask, u32 value)
>>> +{
>>> +     return axi_cc_write32_masked(cc, AXI_CC_GPIOCTL, mask, value);
>>> +}
>>> +EXPORT_SYMBOL(xaxi_chipco_gpio_control);
>>
>> "xaxi"?  Shouldn't that be consistant with the other exports and start
>> with "axi"?
>
> Left from old tests/rewrites/splitting. Thanks.
>
>
>>> +static u8 axi_host_pci_read8(struct axi_device *core, u16 offset)
>>> +{
>>> +     if (unlikely(core->bus->mapped_core != core))
>>
>> Are you sure about the use of unlikely in this, and other functions?
>> The compiler almost always does a better job than we do for these types
>> of calls, just let it do it's job.
>>
>>> +             axi_host_pci_switch_core(core);
>>> +     return ioread8(core->bus->mmio + offset);
>>
>> I think because of that unlikely, you just slowed down all pci devices,
>> right?  That's not very nice :)
>
> Hm, my logic suggests it is alright, but please consider this once
> more with me ;)
>
> For the most of the time mapped_core (active core) do not change. We
> perform few hundreds of operations on one core in a row. This way
> mapped_core points to passed core for most of the time. Condition
> (mapped_core != core) is unlikely to happen.
>
> Is there anything wrong in my logic?
>
> --
> Rafał
> --
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