If you want to do something like this (opinions about usefulnes will probably differ - I'm not going to discuss this here), you don't need to add special commands. You should be able to use the existing commands, eventually packed into a macro definition.
* It is not a special command, it is a configurable side effect of reading/writing to dataflash.
* running mkimage on the host will of course generate the crc check but U-boot does not know that they thing you are copying to storage is an image so it will not check crc automatically.
For your recommendation to work, people have to suspect that the things stored in flash is bad. In my experience, people do not realize that the image is bad, and think they have made a mistake when generating the kernel or the root fs and spend significant time trying to figure out what the problem is and then call me. If I generate/check the crc on all writes/reads, then this support problem will more or less go away. With your proposal, the support problem will remain.
I can of course generate macros, but again, people will want to do their own macros, and they will run into the problem.
Reducing support, is very important, and is worth the extra code space needed.
By doing the crc check when copying from the dataflash to SDRAM you immediately pinpoint the problem.
I don't understand why your appended CRC word is in any way better than our embedded / prepended one, the result of the check will be the same in each case. If you need check the CRC independetly from the boot command, you can always use the "imi" command, or "crc" itself.
If U-Boot contained a command to write the kernel to dataflash, then this command could check that the image fits into the partition allocated for the kernel, and would report a "kernel too large" warning message.
This is not an issue of a special write command, but of such a concept of partitions in flash memory which, at the moment, does not exist.
The current dataflash drivers divides the flash into partitions.
In my private version, the partitions can have a name, and the address of the partition is automatically stored in an environment variable with this name,
It would be fairly easy to implement a command which flashes the kernel/rootfs, to check that they fit into the named partition.
Best regards,
Wolfgang Denk