linux-kernel - Re: [PATCH] fpga: Add flag to indicate SPI bitstream is bit-reversed

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Message-ID: <1665918.lT4CrqcDtW@jclayton-pc>
Date:   Wed, 17 May 2017 07:47:42 -0700
From:   joshua.clayton@...west.com
To:     Anatolij Gustschin <agust@...x.de>
Cc:     linux-fpga@...r.kernel.org, Alan Tull <atull@...nel.org>,
        Moritz Fischer <moritz.fischer@...us.com>,
        linux-kernel@...r.kernel.org,
        Joshua Clayton <stillcompiling@...il.com>
Subject: Re: [PATCH] fpga: Add flag to indicate SPI bitstream is bit-reversed

Hi Alanatolij,
I was just finally able to test this and your other change yesterday	

On Thursday, April 20, 2017 11:43:01 PM PDT Anatolij Gustschin wrote:
> Add a flag that is passed to the write_init() callback,
> indicating that the SPI bitstream starts with LSB first.
> SPI controllers usually send data with MSB first. If an
> FPGA expects bitstream data as LSB first, the data must
> be reversed either by the SPI controller or by the driver.
> 
> Alternatively the bitstream could be prepared as bit-reversed
> to avoid the bit-swapping while sending. This flag indicates
> such bit-reversed SPI bitstream. The low-level driver will
> deal with the flag and perform bit-reversing if needed.
> 
> Signed-off-by: Anatolij Gustschin <agust@...x.de>
> ---
>  include/linux/fpga/fpga-mgr.h | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/include/linux/fpga/fpga-mgr.h b/include/linux/fpga/fpga-mgr.h
> index b4ac24c..5a055a0 100644
> --- a/include/linux/fpga/fpga-mgr.h
> +++ b/include/linux/fpga/fpga-mgr.h
> @@ -67,10 +67,13 @@ enum fpga_mgr_states {
>   * FPGA Manager flags
>   * FPGA_MGR_PARTIAL_RECONFIG: do partial reconfiguration if supported
>   * FPGA_MGR_EXTERNAL_CONFIG: FPGA has been configured prior to Linux
> booting + * FPGA_MGR_SPI_BITSTREAM_LSB_FIRST: SPI bitstream bit order is
> reversed to + *				     start with LSB first
>   */
>  #define FPGA_MGR_PARTIAL_RECONFIG	BIT(0)
>  #define FPGA_MGR_EXTERNAL_CONFIG	BIT(1)
>  #define FPGA_MGR_ENCRYPTED_BITSTREAM	BIT(2)
> +#define FPGA_MGR_SPI_BITSTREAM_LSB_FIRST	BIT(3)
My  thought here is that  FPGA_MGR_BITSTREAM_LSB_FIRST
is a bit shorter, adequate, and could do if another upload method
happened to use LSB first organized data.

> 
>  /**
>   * struct fpga_image_info - information specific to a FPGA image

I'll preparing an updated patch series including a version of your patches
-- 
~Joshua A Clayton