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

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Date:	Wed, 13 Apr 2011 21:39:54 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	Greg KH <greg@...ah.com>
Cc:	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

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.


>> +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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