Re: [RFC/PATCH 0/2] spi: spi-dw: Select 16b or 32b register access

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

On Wed, 2015-03-04 at 16:01 -0600, Thor Thayer wrote:
> Hi Andy,
> 
> On 03/04/2015 02:44 PM, Andy Shevchenko wrote:
> > On Wed, 2015-03-04 at 14:31 -0600, tthayer@xxxxxxxxxxxxxxxxxxxxx wrote:
> >> From: Thor Thayer <tthayer@xxxxxxxxxxxxxxxxxxxxx>
> >>
> >> The Altera Arria10 SoC requires 32 bit accesses to peripherals. The
> >> DesignWare SPI peripheral registers are on 32bit boundaries so this
> >> patch is minimal. Function pointers are used to select 32bit access
> >> or 16bit accesses.
> >
> >
> > So, what is exactly the issue when we read only half of the register?
> > Bus lock, or what?
> >
> 
> The read actually works on our chip but I changed both read and write to 
> be consistent. For Arria10, on a 16 bit write the data isn't written 
> into the DesignWare register.

How did you exactly check this?

> 
> In reply to your other email, yes it does support the DW_apb_ssi but the 
> Arria10 architecture requires 32 bit access (actually as you point out, 
> 32 bit writes). We're using the original driver on our older chips but 
> Arria10 requires upstream changes.

Can you check if the following helps in your case:

--- a/drivers/spi/spi-dw.h
+++ b/drivers/spi/spi-dw.h
@@ -170,6 +170,8 @@ static inline u16 dw_readw(struct dw_spi *dws, u32 offset)
 static inline void dw_writew(struct dw_spi *dws, u32 offset, u16 val)
 {
        __raw_writew(val, dws->regs + offset);
+       mmiowb():
+       __raw_readw(dws->regs + offset);
 }
 
 static inline void spi_enable_chip(struct dw_spi *dws, int enable)

-- 
Andy Shevchenko <andriy.shevchenko@xxxxxxxxx>
Intel Finland Oy

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