linux-kernel - RE: [char-misc-next 07/15] mei: use wrietl/readl instead of io wrappers

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Date:	Tue, 4 Dec 2012 15:28:23 +0000
From:	"Winkler, Tomas" <tomas.winkler@...el.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"arnd@...db.de" <arnd@...db.de>,
	"alan@...ux.intel.com" <alan@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Stanislaw Gruszka <sgruszka@...hat.com>
Subject: RE: [char-misc-next 07/15] mei: use wrietl/readl instead of io
 wrappers

> >
> >  /**
> > @@ -451,7 +451,7 @@ static inline u32 mei_reg_read(const struct
> > mei_device *dev,  static inline void mei_reg_write(const struct mei_device
> *dev,
> >  				 unsigned long offset, u32 value)  {
> > -	iowrite32(value, dev->mem_addr + offset);
> > +	writel(value, dev->mem_addr + offset);
> 
> ioremap should match readl/writel
> iomap iowrite32/ioread32

Thanks, I can replace pci_iomap with pci_ioremap_bar although in low level it is doing just the same.


> so you need to tweak the map/unmap if you do this.
> 
> As to overhead. I'd love to see a measurement that can detect the
> difference. Do you have a benchmark that shows it ?

Don't have any numbers but it seems reasonable to me.
 I did following this example

commit 05f5b97ee0013fefbd9139cf8c3eda5f2a88c04a
Author: Stanislaw Gruszka <sgruszka@...hat.com>
Date:   Wed Mar 7 09:52:26 2012 -0800
 
    iwlwifi: use writeb,writel,readl directly
    
    That change will save us some CPU cycles at run time. Having port-based
    I/O seems to be not possible for PCIe devices.
    
    Signed-off-by: Stanislaw Gruszka <sgruszka@...hat.com>

Thanks
Tomas

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