From mboxrd@z Thu Jan 1 00:00:00 1970 From: Wolfgang Grandegger Subject: Re: [PATCH net-next v2 2/4] can: cc770: add legacy ISA bus driver for the CC770 and AN82527 Date: Tue, 10 Jan 2012 10:30:58 +0100 Message-ID: <4F0C0552.5080504@grandegger.com> References: <4F0B608D.6090309@essax.com> <4F0B7421.6050203@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from ngcobalt02.manitu.net ([217.11.48.102]:44231 "EHLO ngcobalt02.manitu.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754424Ab2AJJbb (ORCPT ); Tue, 10 Jan 2012 04:31:31 -0500 In-Reply-To: <4F0B7421.6050203@pengutronix.de> Sender: linux-can-owner@vger.kernel.org List-ID: To: Marc Kleine-Budde Cc: info@essax.com, David Laight , Oliver Hartkopp , henrik@proconx.com, netdev@vger.kernel.org, linux-can@vger.kernel.org, socketcan-users@lists.berlios.de, IreneV , Stanislav Yelenskiy , oe@port.de, henrik@focus-sw.com 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. >> 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); >> + > > 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. Wolfgang.