linux-kernel - Re: [PATCH RFC] c_can_pci: generic module for c

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Date:	Tue, 05 Jun 2012 13:19:26 +0200
From:	Federico Vaga <federico.vaga@...il.com>
To:	Bhupesh SHARMA <bhupesh.sharma@...com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Wolfgang Grandegger <wg@...ndegger.com>,
	Marc Kleine-Budde <mkl@...gutronix.de>,
	Giancarlo ASNAGHI <giancarlo.asnaghi@...com>,
	Alan Cox <alan@...ux.intel.com>,
	Alessandro Rubini <rubini@...dd.com>,
	"linux-can@...r.kernel.org" <linux-can@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] c_can_pci: generic module for c_can on PCI

> In some of these SoC's the C_CAN registers which are essentially
> 16-bit or 32-bit registers are aligned always to a 32-bit boundary
> (i.e. even a 16-bit register is aligned to 32-bit boundary).
> 
> So, I had to implement two variants of the read/write reg routines. I
> am not sure your SoC implementation needs them. If it does, I will
> categorize it as flaky as well :)

My implementation is align to 32, but I'm trying to make a generic PCI 
wrapper (some other could be aligned to 16)
 
> See above. There was a reason for keeping these routines in
> c_can_platform.c Simply put, every platform having a Bosch C_CAN
> module can have it's own implementation of the bus (for example you
> use PCI) and register bank layout (16-bit or 32-bit aligned).

I don't understand the reason to keep these functions in 
c_can_platform.c . Two generic read/write functions could be written 
into c_can.c by using a shift value (0 if aligned to 16, 1 if aligned to 
32) as I showed in the previous mail:

> > static u16 c_can_read_reg(struct c_can_priv *priv, enum reg index)
> > {
> > 
> > 	return readw(priv->base + (priv->regs[index] << priv->offset));
> > 
> > }
> > static void c_can_write_reg(struct c_can_priv *priv, enum reg index,
> > 
> > 						u16 val)
> > 
> > {
> > 
> > 	writew(val, priv->base + (priv->regs[index] << priv->offset));
> > 
> > }

Every platform having a Bosch C_CAN/D_CAN can specify its shift value (0 
or 1) and it's done.

-- 
Federico Vaga
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