netdev - Re: [PATCH net-next v2 2/4] can: cc770: add legacy ISA bus driver for the CC770 and AN82527

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Date:	Tue, 10 Jan 2012 15:25:17 +0100
From:	Wolfgang Grandegger <wg@...ndegger.com>
To:	info@...ax.com
CC:	Marc Kleine-Budde <mkl@...gutronix.de>,
	David Laight <David.Laight@...LAB.COM>,
	Oliver Hartkopp <socketcan@...tkopp.net>, henrik@...conx.com,
	netdev@...r.kernel.org, linux-can@...r.kernel.org,
	socketcan-users@...ts.berlios.de, IreneV <boir1@...dex.ru>,
	Stanislav Yelenskiy <stanislavelensky@...oo.com>, oe@...t.de,
	henrik@...us-sw.com
Subject: Re: [PATCH net-next v2 2/4] can: cc770: add legacy ISA bus driver
 for the CC770 and AN82527

On 01/10/2012 03:20 PM, Wolfgang Grandegger wrote:
> On 01/10/2012 01:30 PM, Wolfgang Zarre wrote:
>> Hello Wolfgang,
>>
>>> On 01/10/2012 12:11 AM, Marc Kleine-Budde wrote:
>>>> On 01/09/2012 10:47 PM, Wolfgang Zarre wrote:
>>>> [...]
>>>>
>>>>>>> OK. My concern: Can we be sure that 16bit accesses are always
>>>>>> supported
>>>>>>> by the hardware? Does a spinlock_irqsave/spinlock_irqrestore around
>>>>>> the
>>>>>>> 8bit accesses already help?
>>>>>>
>>>>>> Hmmm... are there any register reads that need the
>>>>>> same 'double cycle' sequence ??
>>>>>> If so you need to stop reads being interleaved (with
>>>>>> themselves and writes) so requesting a 16bit access
>>>>>> doesn't help.
>>>>>>
>>>>>> Which means you need a spinlock...
>>>>>>
>>>>>>      David
>>>>>>
>>>>>>
>>>>>
>>>>> @David: Thank You very much for that hint. You are right and to
>>>>> implement correct we need a spinlock.
>>>>>
>>>>> @Wolfgang: I was thinking about Your question regarding 8/16 bit and
>>>>> in fact it wouldn't work at all on a clean 8 bit cards.
>>>>>
>>>>> Further it wouldn't work on 16 bit cards where the MSB is not equal
>>>>> to base port +1 and anyway, it's depending always on how the chip is
>>>>> interfaced to the ISA bus and in which mode the chip is configured.
>>>>>
>>>>>
>>>>> And therefore I was giving David's hint a try in using a spinlock in
>>>>> function cc770_isa_port_write_reg_indirect() and patched as follows:
>>>>>
>>>>> ---------------------------------------------------------------------
>>>>> diff --git a/drivers/net/can/cc770/cc770.c
>>>>> b/drivers/net/can/cc770/cc770.c
>>>>> index 2d12f89..dad6707 100644
>>>>> --- a/drivers/net/can/cc770/cc770.c
>>>>> +++ b/drivers/net/can/cc770/cc770.c
>>>>> @@ -460,15 +460,6 @@ static netdev_tx_t cc770_start_xmit(struct sk_buff
>>>>> *skb, struct net_device *dev)
>>>>>
>>>>>       stats->tx_bytes += dlc;
>>>>>
>>>>> -
>>>>> -    /*
>>>>> -     * HM: We had some cases of repeated IRQs so make sure the
>>>>> -     * INT is acknowledged I know it's already further up, but
>>>>> -     * doing again fixed the issue
>>>>> -     */
>>>>> -    cc770_write_reg(priv, msgobj[mo].ctrl0,
>>>>> -            MSGVAL_UNC | TXIE_UNC | RXIE_UNC | INTPND_RES);
>>>>> -
>>>>>       return NETDEV_TX_OK;
>>>>>   }
>>>>>
>>>>> @@ -689,12 +680,6 @@ static void cc770_tx_interrupt(struct net_device
>>>>> *dev, unsigned int o)
>>>>>       /* Nothing more to send, switch off interrupts */
>>>>>       cc770_write_reg(priv, msgobj[mo].ctrl0,
>>>>>               MSGVAL_RES | TXIE_RES | RXIE_RES | INTPND_RES);
>>>>> -    /*
>>>>> -     * We had some cases of repeated IRQ so make sure the
>>>>> -     * INT is acknowledged
>>>>> -     */
>>>>> -    cc770_write_reg(priv, msgobj[mo].ctrl0,
>>>>> -            MSGVAL_UNC | TXIE_UNC | RXIE_UNC | INTPND_RES);
>>>
>>> Please provide an extra patch for these unrelated changes. If we really
>>> want to remove it.
>>>
>>
>> Sure, this I can do.
>>
>>>>>       stats->tx_packets++;
>>>>>       can_get_echo_skb(dev, 0);
>>>>> diff --git a/drivers/net/can/cc770/cc770_isa.c
>>>>> b/drivers/net/can/cc770/cc770_isa.c
>>>>> index 4be5fe2..fe39eed 100644
>>>>> --- a/drivers/net/can/cc770/cc770_isa.c
>>>>> +++ b/drivers/net/can/cc770/cc770_isa.c
>>>>> @@ -110,6 +110,9 @@ MODULE_PARM_DESC(bcr, "Bus configuration register
>>>>> (default=0x40 [CBY])");
>>>>>   #define CC770_IOSIZE          0x20
>>>>>   #define CC770_IOSIZE_INDIRECT 0x02
>>>>>
>>>>> +/* Spinlock for cc770_isa_port_write_reg_indirect */
>>>>> +static DEFINE_SPINLOCK( outb_lock);
> 
> Please use a more specific name, e.g.: cc770_isa_port_lock
> 
>>>>> +
>>>>
>>>> Do we need a global or a per device spin lock? If this should be a per
>>>> device one, please introduce a cc770_isa_priv and put the spinlock
>>>> there. Don't forget to initialize the spinlock.
>>>
>>> Yes, that's what I was thinking as well but in the ocan driver I find:
>>>
>>> /*
>>>   * we need a spinlock here, as the address register looks shared between
>>>   * two PC-ECAN devices. Moreover, we need to protect WRT interrupts
>>>   */
>>>
>>> Looks like wired hardware. Anyway, a global spinlock might be safer.
>>>
>>
>> Hmmm, actually I thought to place the spinlock local because of having
>> the problem just with the interrupt and not with mutex.
>>
>> But if global wouldn't it then better to make an array[MAX_DEV] for the
>> lock with initialisation in _init or _start?
> 
> Global means *one* spin-irq-lock for the indirect register access of all
> devices. That might be the most efficient solution but we are sure that

s/might/might not/

> it works, also with wired i82527 hardware, which seem to exist. That's
> also what the related lincan and ocan drivers used.

Wolfgang.
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