[U-Boot] [PATCH 04/31] powerpc: 82xx serial: add configurable SMC Rx buffer len

[Heiko Schocher <hs@denx.de>]

Hello Wolfgang,

Wolfgang Denk wrote:
> In message <498027A8.3010200@denx.de> you wrote:
>> This patch adds the configuration option CONFIG_SYS_SMC_RXBUFLEN.
> 
> We discussed this before. I explained that I do not want to have this
> added level of complexity in the driver.
> 
> Why should I reconsider?

Hups, seems I missed something (Seems I stepped into this subject, after
it was discussed here). I thought that you didnt want such a try, because
it changes a driver that a lot of boards uses, and if this change is
manageable it has a chance to get in mainline. Sorry, I have a look
in the archives ...

>> With this option it is possible to allow the receive
>> buffer for the SMC on 82xx to be greater then 1. In case
> 
> How is this supposed to work?
> 
> Assume you set CONFIG_SYS_SMC_RXBUFLEN to 4, and the user at the
> serial console port enters just a single character. When will the
> receiver return this character? You might want to explain the
> setup...

He will become this character when an idle-timout occurs. Then
the SMC closes the buffer ...

> More technical comments below.
> 
>>  cpu/mpc8260/serial_smc.c |   94 +++++++++++++++++++++++++++++++---------------
>>  include/configs/mgcoge.h |    1 +
>>  2 files changed, 64 insertions(+), 31 deletions(-)
>>
>> diff --git a/cpu/mpc8260/serial_smc.c b/cpu/mpc8260/serial_smc.c
>> index a6efa66..6825e2e 100644
>> --- a/cpu/mpc8260/serial_smc.c
>> +++ b/cpu/mpc8260/serial_smc.c
>> @@ -64,6 +64,18 @@ DECLARE_GLOBAL_DATA_PTR;
>>
>>  #endif
>>
>> +typedef volatile struct serialbuffer {
>> +	cbd_t	rxbd;		/* Rx BD */
>> +	cbd_t	txbd;		/* Tx BD */
>> +#ifdef CONFIG_SYS_SMC_RXBUFLEN
>> +	uint	rxindex;	/* index for next character to read */
>> +	volatile uchar	rxbuf[CONFIG_SYS_SMC_RXBUFLEN];/* rx buffers */
>> +#else
>> +	volatile uchar	rxbuf[1];	/* rx buffers */
>> +#endif
> 
> This ifdef can be avoided if you #define CONFIG_SYS_SMC_RXBUFLEN as 1
> as a default value. Makes the code much easir to read.

OK.

>> -	rbdf->cbd_bufaddr = (uint) (rbdf+2);
>> -	rbdf->cbd_sc = 0;
>> -	tbdf = rbdf + 1;
>> -	tbdf->cbd_bufaddr = ((uint) (rbdf+2)) + 1;
>> -	tbdf->cbd_sc = 0;
>> +	rtx->rxbd.cbd_bufaddr = (uint) &rtx->rxbuf;
>> +	rtx->rxbd.cbd_sc      = 0;
>> +
>> +	rtx->txbd.cbd_bufaddr = (uint) &rtx->txbuf;
>> +	rtx->txbd.cbd_sc      = 0;
> 
> The code does not exactly become easier to read. You might consider
> using a pointer instead of rtx->rxbd resp. rtx->txbd - this would
> probably largely reduce the size of your patch.

OK, try this out.

>> +#ifdef CONFIG_SYS_SMC_RXBUFLEN
>> +	/* multi-character receive.
>> +	*/
> 
> Incorrect multiline comment style. Please fix (also some other
> places).

damn. (I have really problems to see such things, when the code is
not complete from my hand ... and I really tried to see such things)

:-(

>> +	up->smc_mrblr = CONFIG_SYS_SMC_RXBUFLEN;
>> +	up->smc_maxidl = 10;
>> +	rtx->rxindex = 0;
>> +#else
>>  	/* Single character receive.
>>  	*/
>>  	up->smc_mrblr = 1;
>>  	up->smc_maxidl = 0;
>> +#endif
> 
> You might want to explain what the magic constant "10" above means. If
> you use a #define for it, you could have it default to 1, and get rid
> of another #ifdef block.

Yes, a define would be much better.

>> +#ifdef CONFIG_SYS_SMC_RXBUFLEN
>> +	/* the characters are read one by one,
>> +	 * use the rxindex to know the next char to deliver
>> +	 */
>> +	c = *(unsigned char *) (rtx->rxbd.cbd_bufaddr+rtx->rxindex);
>> +	rtx->rxindex++;
>> +
>> +	/* check if all char are readout, then make prepare for next receive */
>> +	if (rtx->rxindex >= rtx->rxbd.cbd_datlen) {
>> +		rtx->rxindex = 0;
>> +	rtx->rxbd.cbd_sc |= BD_SC_EMPTY;
>> +	}
> 
> Indentation wrong.

I fix that.

>> +#else
>> +	c = *(unsigned char *) (rtx->rxbd.cbd_bufaddr);
>> +	rtx->rxbd.cbd_sc |= BD_SC_EMPTY;
>> +#endif
>>  	return(c);
> 
> I think this #ifdef can be largely avoided, too, given that
> rtx->rxindex is always 0 in the non-CONFIG_SYS_SMC_RXBUFLEN case.
> 
>> diff --git a/include/configs/mgcoge.h b/include/configs/mgcoge.h
>> index 9416a03..ddb06aa 100644
>> --- a/include/configs/mgcoge.h
>> +++ b/include/configs/mgcoge.h
>> @@ -49,6 +49,7 @@
>>  #undef  CONFIG_CONS_ON_SCC		/* It's not on SCC           */
>>  #undef	CONFIG_CONS_NONE		/* It's not on external UART */
>>  #define CONFIG_CONS_INDEX	2	/* SMC2 is used for console  */
>> +#define CONFIG_SYS_SMC_RXBUFLEN	16
> 
> Did you do any performance measurements? How much performance do
> you really save this way?

I must have a look in old logs

thanks
Heiko
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