Re: [PATCH] mmc_spi: do propper retry managment in the block layer - 3rd try

From: Wolfgang Mües
Date: Thu May 28 2009 - 05:54:46 EST


Am Donnerstag, 28. Mai 2009 schrieb Matt Fleming:
> When I said "report the correct error" I was objecting to using EILSEQ
> as The One True Error Code based on the fact that a transmission error
> may, or may not, have occurred.

Yes, and we have discussed the problem of error code interpretion based on
request types.

So, in block.c, if I get a -EIO (== erase error), I can handle this as
transmission error inside the read/write data function.

If there will be a (future) erase request function in block.c, I will handle
the same error code as erase error, not as transmission error. No big
problems here.

To mimic the same behaviour inside the driver, inside mmc_spi_response_get,
I will have to code:

if (cmd->resp[0] != 0) {
& cmd->resp[0])
// TODO: transmission error if parameter or address was not out of range.
value = -EFAULT; /* Bad address */
else if (R1_SPI_ILLEGAL_COMMAND & cmd->resp[0])
// TODO: transmission error if mandatory command
value = -ENOSYS; /* Function not implemented */
else if (R1_SPI_COM_CRC & cmd->resp[0])
value = -EILSEQ; /* Illegal byte sequence */
& cmd->resp[0])
switch (cmd->opcode) {
case xxx: /* erase commands */
case yyy:
value = -EIO; /* I/O error */
default: /* non-erase commands */
value = -EILSEQ; /* Illegal byte sequence */
/* else R1_SPI_IDLE, "it's resetting" */

So somewhere I will need to have an error code filter based on the issued
command (class). Should this be in the driver(s)? Or should it be at the
location of the caller, in block.c?

The advantages of putting it in block.c is that
a) The command (class) is typically implicit given in the function, and no
need for a switch() statement.
b) Only one handling for different drivers, not scattered through all(?) host

I must admit that I have difficulties to see a clear layering violation.
There is no clear definition of which error codes should be reported to the
block layer. There is only a short list of codes with special meaning, but
not a full list of all used codes.

And some drivers are reporting codes like ENOMEM etc...

I see that Pierre wants to have a more smaller interface between drivers and
the upper layer, reporting only classes of errors, to have a more smaller and
cleaner code in the upper layer. But I think that this is a patch of its own,
and not in the context of the retry patch.

i. A. Wolfgang Mües
Auerswald GmbH & Co. KG
Hardware Development
Telefon: +49 (0)5306 9219 0
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E-Mail: Wolfgang.Mues@xxxxxxxxxxxx
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