i.MX: GPIO based SPI chip selects question

i.MX: GPIO based SPI chip selects question

[Wayne Tams]

Hi,

Can I use GPIO pins on my i.mx53 for SPI chip select, I have found little
on the web that can help me, I am hoping that it is straight-forward enough
for me to implement it? Perhaps there is a macro that I can use in the
spi_board_info structure that will let me declare the GPIO?

If it is not possible, could anyone offer a suggestion on a solution for
adding more chips selects, perhaps there is another platform out there that
implements this sort of GPIO functionality?

Many thanks

Wayne
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Re: i.MX: GPIO based SPI chip selects question

[Grant Likely]

On Fri, Oct 28, 2011 at 02:06:16PM +0100, Wayne Tams wrote:
> Hi,
> 
> Can I use GPIO pins on my i.mx53 for SPI chip select, I have found little
> on the web that can help me, I am hoping that it is straight-forward enough
> for me to implement it? Perhaps there is a macro that I can use in the
> spi_board_info structure that will let me declare the GPIO?

Yes, you can, but you may need to modify the spi driver to twiddle
gpios between transfers.  Not all drivers have it implemented.

Bonus points if you create a generic gpio ss handling hook that all
the spi drivers can use.

g.

> 
> If it is not possible, could anyone offer a suggestion on a solution for
> adding more chips selects, perhaps there is another platform out there that
> implements this sort of GPIO functionality?
> 
> Many thanks
> 
> Wayne
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> demand for specialized networking skills is growing even more rapidly.
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Re: i.MX: GPIO based SPI chip selects question

[Baruch Siach]

Hi Wayne,

On Fri, Oct 28, 2011 at 02:06:16PM +0100, Wayne Tams wrote:
> Can I use GPIO pins on my i.mx53 for SPI chip select, I have found little
> on the web that can help me, I am hoping that it is straight-forward enough
> for me to implement it? Perhaps there is a macro that I can use in the
> spi_board_info structure that will let me declare the GPIO?

If you are using the mainline kernel then the SPI driver 
(drivers/spi/spi-imx.c) supports the use of GPIO lines for chip-select 
exclusively. You can find an i.MX53 specific example in 
arch/arm/mach-mx5/board-mx53_evk.c (look for the mx53_evk_spi_data struct).  
This example demonstrate the use of two GPIOs for chip-select, but the list of 
chip-selects can be longer.

Since you appear to be using the Freescale supplied kernel (as I infer from 
your previous question on this list), you are probably using different driver.  
This driver (likely 
http://opensource.freescale.com/git?p=imx/linux-2.6-imx.git;a=blob;f=drivers/spi/mxc_spi.c;h=8c722686a0e1a419b417c0e2f98a4d6f028cf02e;hb=a1cd8a787a18da69ac4e48cfc876623bd7323799) 
does not support GPIOs for chip-select.

Freescale seem to have abandoned their in-house non mainlined SPI driver in a 
later version of their kernel (rel_imx_2.6.38_11.09.01 tag in 
http://opensource.freescale.com/git) so you may want to update your kernel.

baruch

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Re: i.MX: GPIO based SPI chip selects question

[Wayne Tams]

On Sat, Oct 29, 2011 at 9:44 PM, Baruch Siach <baruch-NswTu9S1W3P6gbPvEgmw2w@public.gmane.org> wrote:
> Hi Wayne,
>
> On Fri, Oct 28, 2011 at 02:06:16PM +0100, Wayne Tams wrote:
>> Can I use GPIO pins on my i.mx53 for SPI chip select, I have found little
>> on the web that can help me, I am hoping that it is straight-forward enough
>> for me to implement it? Perhaps there is a macro that I can use in the
>> spi_board_info structure that will let me declare the GPIO?
>
> If you are using the mainline kernel then the SPI driver
> (drivers/spi/spi-imx.c) supports the use of GPIO lines for chip-select
> exclusively. You can find an i.MX53 specific example in
> arch/arm/mach-mx5/board-mx53_evk.c (look for the mx53_evk_spi_data struct).
> This example demonstrate the use of two GPIOs for chip-select, but the list of
> chip-selects can be longer.

That looks promising, I assume you mean that your quoted example makes
use of the driver spi-imx?
>
> Since you appear to be using the Freescale supplied kernel (as I infer from
> your previous question on this list), you are probably using different driver.
> This driver (likely
> http://opensource.freescale.com/git?p=imx/linux-2.6-imx.git;a=blob;f=drivers/spi/mxc_spi.c;h=8c722686a0e1a419b417c0e2f98a4d6f028cf02e;hb=a1cd8a787a18da69ac4e48cfc876623bd7323799)
> does not support GPIOs for chip-select.

I should of added that I am using a kernel from a BSP supplied by
Emtrion, as you guessed correctly, it based on the Freescale kernel
which uses the mxc_spi driver.
>
> Freescale seem to have abandoned their in-house non mainlined SPI driver in a
> later version of their kernel (rel_imx_2.6.38_11.09.01 tag in
> http://opensource.freescale.com/git) so you may want to update your kernel.

I will have a look at how much of an impact using the mainlined kernel
will have on the operation of my SoM. A little off topic, bearing in
mind my inexperience with Linux, can I upgrade the kernel using git
and will the differences between the mainlined and Emtrion kernel be
highlighted? It is just that there could be some Emtrion kernel adds
that I could miss which may impact my board operation, memory mapping
etc.

Just to summarise, are these the options available to me? If so I will
figure out which method will be best for me to do:

1) Hack the existing mxc_spi driver and add support for GPIO chip-select
2) Upgrade the kernel to the latest mainlined version and use the
spi-imx driver included in that
3) Hack the kernel to use the spi_imx driver already included in the
BSP which has GPIO chip-select support
4) Update my BSP SPI driver to the mainlined version

Thank you for your help Baruch (and Grant) much appreciated,
>
> baruch
>
> --
>                                                     ~. .~   Tk Open Systems
> =}------------------------------------------------ooO--U--Ooo------------{=
>   - baruch-NswTu9S1W3P6gbPvEgmw2w@public.gmane.org - tel: +972.2.679.5364, http://www.tkos.co.il -
>

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Re: i.MX: GPIO based SPI chip selects question

[Baruch Siach]

Hi Wayne,

On Mon, Oct 31, 2011 at 09:26:25AM +0000, Wayne Tams wrote:
> On Sat, Oct 29, 2011 at 9:44 PM, Baruch Siach <baruch-NswTu9S1W3P6gbPvEgmw2w@public.gmane.org> wrote:
> > On Fri, Oct 28, 2011 at 02:06:16PM +0100, Wayne Tams wrote:
> >> Can I use GPIO pins on my i.mx53 for SPI chip select, I have found little
> >> on the web that can help me, I am hoping that it is straight-forward enough
> >> for me to implement it? Perhaps there is a macro that I can use in the
> >> spi_board_info structure that will let me declare the GPIO?
> >
> > If you are using the mainline kernel then the SPI driver
> > (drivers/spi/spi-imx.c) supports the use of GPIO lines for chip-select
> > exclusively. You can find an i.MX53 specific example in
> > arch/arm/mach-mx5/board-mx53_evk.c (look for the mx53_evk_spi_data struct).
> > This example demonstrate the use of two GPIOs for chip-select, but the list of
> > chip-selects can be longer.
> 
> That looks promising, I assume you mean that your quoted example makes
> use of the driver spi-imx?

Yes.

> > Since you appear to be using the Freescale supplied kernel (as I infer from
> > your previous question on this list), you are probably using different driver.
> > This driver (likely
> > http://opensource.freescale.com/git?p=imx/linux-2.6-imx.git;a=blob;f=drivers/spi/mxc_spi.c;h=8c722686a0e1a419b417c0e2f98a4d6f028cf02e;hb=a1cd8a787a18da69ac4e48cfc876623bd7323799)
> > does not support GPIOs for chip-select.
> 
> I should of added that I am using a kernel from a BSP supplied by
> Emtrion, as you guessed correctly, it based on the Freescale kernel
> which uses the mxc_spi driver.
> >
> > Freescale seem to have abandoned their in-house non mainlined SPI driver in a
> > later version of their kernel (rel_imx_2.6.38_11.09.01 tag in
> > http://opensource.freescale.com/git) so you may want to update your kernel.
> 
> I will have a look at how much of an impact using the mainlined kernel
> will have on the operation of my SoM. A little off topic, bearing in
> mind my inexperience with Linux, can I upgrade the kernel using git
> and will the differences between the mainlined and Emtrion kernel be
> highlighted? It is just that there could be some Emtrion kernel adds
> that I could miss which may impact my board operation, memory mapping
> etc.

Very likely. You'll probably need to port Emtrion's platform code (you'll find 
it under arch/arm/mach-mx5/) to the mainline kernel. This is quite off topic 
here though. i.MX platform related discussions should go to the 
linux-arm-kernel list.

> Just to summarise, are these the options available to me? If so I will
> figure out which method will be best for me to do:
> 
> 1) Hack the existing mxc_spi driver and add support for GPIO chip-select
> 2) Upgrade the kernel to the latest mainlined version and use the
> spi-imx driver included in that
> 3) Hack the kernel to use the spi_imx driver already included in the
> BSP which has GPIO chip-select support
> 4) Update my BSP SPI driver to the mainlined version

An option similar to (4) is to just use the spi-imx driver that is present in 
your current Emtrion supplied kernel. Just select it instead of mxc_spi.  
You'll need to adjust Emtrion's platform code accordingly.

The option I actually meant to suggest is to use the Freescale supplied 
rel_imx_2.6.38_11.09.01 kernel, that presumably includes some not yet 
mainlined drivers that you may need, while still using the GPIOs enabled 
mainline spi-imx driver.

baruch

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=}------------------------------------------------ooO--U--Ooo------------{=
   - baruch-NswTu9S1W3P6gbPvEgmw2w@public.gmane.org - tel: +972.2.679.5364, http://www.tkos.co.il -

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