Re: Aw: [PATCH v5 3/4] tpm/st33zp24/spi: Add st33zp24 spi phy

[RICARD Christophe <christophe.ricard-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hi Peter,

A TPM command can be up to 2048 byte, A TPM response can be up to 1024 byte.
Between command and response, there are latency byte (up to 15 usually 
on st33zp24 2 are enough).

Overall when sending a command and expecting an answer we need in worst 
case:
2048 (for the TPM command) + 1024 (for the TPM answer).  We need some 
latency byte before the answer is available (max 15).
We have 2048 + 1024 + 15.

I will go for a define making the code more readable together with a 
comment.

Best Regards
Christophe
Le 28/01/2015 17:48, Peter Huewe a écrit :
> Hi Christophe,
>
> sorry to be nitty picky but I still don't get this calculation
>
>
> + /* max tpm tx buffer(TPM_BUFSIZE) + max tpm rx buffer(TPM_BUFSIZE / 2)
> + * + MAX_SPI_LATENCY.
> + */
> + phy->spi_xfer.tx_buf = devm_kmalloc(&dev->dev, (TPM_BUFSIZE +
> + (TPM_BUFSIZE / 2) + MAX_SPI_LATENCY),
> + GFP_KERNEL);
> + if (!phy->spi_xfer.tx_buf)
> + return -ENOMEM;
> +
> + phy->spi_xfer.rx_buf = devm_kmalloc(&dev->dev, (TPM_BUFSIZE +
> + (TPM_BUFSIZE / 2) + MAX_SPI_LATENCY),
> + GFP_KERNEL);
> + if (!phy->spi_xfer.rx_buf)
> + return -ENOMEM;
>   
>
> and the comment
> + /* max tpm tx buffer(TPM_BUFSIZE) + max tpm rx buffer(TPM_BUFSIZE / 2)
> + * + MAX_SPI_LATENCY.
> does not help either.
>
>
>
> Why do you define TPM_BUFSIZE as 2048, add TPM_BUFSIZE/2 and something called MAX_SPI_LATENCY to it to use it as your buffer size?
> Latency is for me something timing related.
>
> Since you use this TPM_BUFSIZE only in these two lines I'd be happy with either
> define which has this magical 2048+2014+15
> or (maybe better) add a reasonable comment describing the meaning of this strange calculation.
>
>
> Thanks,
> Peter

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