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

On Wed, 2015-03-04 at 16:01 -0600, Thor Thayer wrote:

Hi Andy,

On 03/04/2015 02:44 PM, Andy Shevchenko wrote:

quoted

On Wed, 2015-03-04 at 14:31 -0600, tthayer-yzvPICuk2ABMcg4IHK0kFoH6Mc4MB0Vx@public.gmane.org wrote:

quoted

From: Thor Thayer <redacted>

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-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Intel Finland Oy

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