can: tcan4x5x: spi bits_per_word issue on Raspberry PI

can: tcan4x5x: spi bits_per_word issue on Raspberry PI

[FIXED-TERM Buecheler Konstantin (ETAS-SEC/ECT-Mu)]

Hi all,

I am trying to use a tcan4550 together with a Raspberry PI 3 B. I am using the tcan4x5x driver from net-next. 
I always get the following error during startup.
	tcan4x5x spi0.0: Probe failed, err=-22
	tcan4x5x: probe of spi0.0 failed with error -22

I realized that this happens because the Raspberry PI does only support 8/9 bit words. https://elinux.org/index.php?title=RPi_SPI#Supported_bits_per_word
In the driver it is set to 32.
	spi->bits_per_word = 32;

Setting this to 8 does not help of course since the tcan chip expects a multiple of 32 per spi transaction. 
I don't know if this is a Raspberry Pi specific problem or if there are more devices with this hardware limitation. 

Does anyone have a workaround for that? 

If this a common issue it might be a good idea to patch the driver. I will check if I can find proper a way to do so. 

Regards, 
Konstantin 

can: tcan4x5x: spi bits_per_word issue on Raspberry PI

[FIXED-TERM Buecheler Konstantin (ETAS-SEC/ECT-Mu)]

Hi all,

I am trying to use a tcan4550 together with a Raspberry PI 3 B. I am using the tcan4x5x driver from net-next. 
I always get the following error during startup.
	tcan4x5x spi0.0: Probe failed, err=-22
	tcan4x5x: probe of spi0.0 failed with error -22

I realized that this happens because the Raspberry PI does only support 8/9 bit words. https://elinux.org/index.php?title=RPi_SPI#Supported_bits_per_word
In the driver it is set to 32.
	spi->bits_per_word = 32;

Setting this to 8 does not help of course since the tcan chip expects a multiple of 32 per spi transaction. 
I don't know if this is a Raspberry Pi specific problem or if there are more devices with this hardware limitation. 

Does anyone have a workaround for that? 

If this a common issue it might be a good idea to patch the driver. I will check if I can find proper a way to do so. 

Regards, 
Konstantin 

Re: can: tcan4x5x: spi bits_per_word issue on Raspberry PI

[Marc Kleine-Budde]

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On 8/14/19 5:01 PM, FIXED-TERM Buecheler Konstantin (ETAS-SEC/ECT-Mu) wrote:
>> Hi all,
>>
>> I am trying to use a tcan4550 together with a Raspberry PI 3 B. I am using the
>> tcan4x5x driver from net-next.
>> I always get the following error during startup.
>> 	tcan4x5x spi0.0: Probe failed, err=-22
>> 	tcan4x5x: probe of spi0.0 failed with error -22
>>
>> I realized that this happens because the Raspberry PI does only support 8/9 bit
>> words. https://elinux.org/index.php?title=RPi_SPI#Supported_bits_per_word
>> In the driver it is set to 32.
>> 	spi->bits_per_word = 32;
>>
>> Setting this to 8 does not help of course since the tcan chip expects a multiple of
>> 32 per spi transaction.
>> I don't know if this is a Raspberry Pi specific problem or if there are more devices
>> with this hardware limitation.
>>
>> Does anyone have a workaround for that?
> 
> It seems to be enough to just change the bits_per_word value to 8
> 
>>
>> If this a common issue it might be a good idea to patch the driver. I will check if I
>> can find proper a way to do so.
>>
>> Regards,
>> Konstantin
> 
> Now I have another really confusing problem. Anything I write to SPI is written little endian. The tcan chip expects big endian. 
> Anything I read from SPI is treated as little endian but is big endian. Does anyone know why this happens? 
> Is there a flag or something I can set for the SPI device/wire to fix this?

Have you changed the bits_per_word to 8? Then you read just a stream of
bytes. If you tread them as an u32 they are in host order.

Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |


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Re: can: tcan4x5x: spi bits_per_word issue on Raspberry PI

[Marc Kleine-Budde]

[-- Attachment #1.1: Type: text/plain, Size: 1871 bytes --]

On 8/14/19 5:01 PM, FIXED-TERM Buecheler Konstantin (ETAS-SEC/ECT-Mu) wrote:
>> Hi all,
>>
>> I am trying to use a tcan4550 together with a Raspberry PI 3 B. I am using the
>> tcan4x5x driver from net-next.
>> I always get the following error during startup.
>> 	tcan4x5x spi0.0: Probe failed, err=-22
>> 	tcan4x5x: probe of spi0.0 failed with error -22
>>
>> I realized that this happens because the Raspberry PI does only support 8/9 bit
>> words. https://elinux.org/index.php?title=RPi_SPI#Supported_bits_per_word
>> In the driver it is set to 32.
>> 	spi->bits_per_word = 32;
>>
>> Setting this to 8 does not help of course since the tcan chip expects a multiple of
>> 32 per spi transaction.
>> I don't know if this is a Raspberry Pi specific problem or if there are more devices
>> with this hardware limitation.
>>
>> Does anyone have a workaround for that?
> 
> It seems to be enough to just change the bits_per_word value to 8
> 
>>
>> If this a common issue it might be a good idea to patch the driver. I will check if I
>> can find proper a way to do so.
>>
>> Regards,
>> Konstantin
> 
> Now I have another really confusing problem. Anything I write to SPI is written little endian. The tcan chip expects big endian. 
> Anything I read from SPI is treated as little endian but is big endian. Does anyone know why this happens? 
> Is there a flag or something I can set for the SPI device/wire to fix this?

Have you changed the bits_per_word to 8? Then you read just a stream of
bytes. If you tread them as an u32 they are in host order.

Marc

-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
Industrial Linux Solutions        | Phone: +49-231-2826-924     |
Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |


[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

can: tcan4x5x: spi bits_per_word issue on Raspberry PI

[FIXED-TERM Buecheler Konstantin (ETAS-SEC/ECT-Mu)]

> Hi all,
> 
> I am trying to use a tcan4550 together with a Raspberry PI 3 B. I am using the
> tcan4x5x driver from net-next.
> I always get the following error during startup.
> 	tcan4x5x spi0.0: Probe failed, err=-22
> 	tcan4x5x: probe of spi0.0 failed with error -22
> 
> I realized that this happens because the Raspberry PI does only support 8/9 bit
> words. https://elinux.org/index.php?title=RPi_SPI#Supported_bits_per_word
> In the driver it is set to 32.
> 	spi->bits_per_word = 32;
> 
> Setting this to 8 does not help of course since the tcan chip expects a multiple of
> 32 per spi transaction.
> I don't know if this is a Raspberry Pi specific problem or if there are more devices
> with this hardware limitation.
> 
> Does anyone have a workaround for that?

It seems to be enough to just change the bits_per_word value to 8

> 
> If this a common issue it might be a good idea to patch the driver. I will check if I
> can find proper a way to do so.
> 
> Regards,
> Konstantin

Now I have another really confusing problem. Anything I write to SPI is written little endian. The tcan chip expects big endian. 
Anything I read from SPI is treated as little endian but is big endian. Does anyone know why this happens? 
Is there a flag or something I can set for the SPI device/wire to fix this?

Regards,
Konstantin

can: tcan4x5x: spi bits_per_word issue on Raspberry PI

[FIXED-TERM Buecheler Konstantin (ETAS-SEC/ECT-Mu)]

> Hi all,
> 
> I am trying to use a tcan4550 together with a Raspberry PI 3 B. I am using the
> tcan4x5x driver from net-next.
> I always get the following error during startup.
> 	tcan4x5x spi0.0: Probe failed, err=-22
> 	tcan4x5x: probe of spi0.0 failed with error -22
> 
> I realized that this happens because the Raspberry PI does only support 8/9 bit
> words. https://elinux.org/index.php?title=RPi_SPI#Supported_bits_per_word
> In the driver it is set to 32.
> 	spi->bits_per_word = 32;
> 
> Setting this to 8 does not help of course since the tcan chip expects a multiple of
> 32 per spi transaction.
> I don't know if this is a Raspberry Pi specific problem or if there are more devices
> with this hardware limitation.
> 
> Does anyone have a workaround for that?

It seems to be enough to just change the bits_per_word value to 8

> 
> If this a common issue it might be a good idea to patch the driver. I will check if I
> can find proper a way to do so.
> 
> Regards,
> Konstantin

Now I have another really confusing problem. Anything I write to SPI is written little endian. The tcan chip expects big endian. 
Anything I read from SPI is treated as little endian but is big endian. Does anyone know why this happens? 
Is there a flag or something I can set for the SPI device/wire to fix this?

Regards,
Konstantin