Question about nand_scan()

DISCUSSION Jan Glauber 2 participants 3 messages Sep 23, 2016 Memory technology devices (MTD)

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Jan Glauber

author

2016-09-23 11:30 UTC #0 lore raw

Hi all,

I'm working on a driver for the NAND controller on Cavium's ThunderX.

So far I implemented the low-level functions for using the controller to access a NAND chip. I can read the ONFI ID and parameter page with that.

Now I wanted to use nand_scan() instead of manually reading the chip parameters, but it fails with "No NAND device found".

The hardware I'm using has one NAND device wired as chip 1 (the NAND controller support chips 0..7).

The reason for the failure seems to be that nand_get_flash_type() returns an error before all the chips are scanned. What I don't understand is in that function chip 0 is selected before the loop that would scan all chips:

        /* Select the device */
        chip->select_chip(mtd, 0);

My select_chip() stores the chip number (in that case 0) and uses that for subsequent commands to the controller. Since there is no chip 0 the read returns nothing and nand_scan() fails.

Probably I'm missing something, would be great if someone could help me...

thanks,
Jan

Boris Brezillon

2016-09-23 11:44 UTC #1 lore raw

Hi Jan,

Quoted 22 lines · On Fri, 23 Sep 2016 13:29:44 +0200 Jan Glauber…

Hi all,
I'm working on a driver for the NAND controller on Cavium's ThunderX.
So far I implemented the low-level functions for using the controller to access a NAND chip. I can read the ONFI ID and parameter page with that.
Now I wanted to use nand_scan() instead of manually reading the chip parameters, but it fails with "No NAND device found".
The hardware I'm using has one NAND device wired as chip 1 (the NAND controller support chips 0..7).
The reason for the failure seems to be that nand_get_flash_type() returns an error before all the chips are scanned. What I don't understand is in that function chip 0 is selected before the loop that would scan all chips:
        /* Select the device */
        chip->select_chip(mtd, 0);

Quoted 6 lines

My select_chip() stores the chip number (in that case 0) and uses that for subsequent commands to the controller. Since there is no chip 0 the read returns nothing and nand_scan() fails.
Probably I'm missing something, would be great if someone could help me...

Actually, the chip parameter passed to ->select_chip() is not the CS-id from the NAND controller PoV, but the one from the NAND chip PoV.

You have to store an association table between chip⁻CS and controller-CS somewhere in your NAND controller private struct (a struct inheriting from nand_control_hw).

And remember that nand_scan_ident() is supposed to detect a single NAND chip, not all the chips connected to your controller (the multi-CS logic is here to handle multi-dies NANDs, not the case where you have multiple NAND chips connected to the same controller).

You can have a look at the sunxi_nand [1] driver if you want an example.

Regards,

Boris

[1]http://lxr.free-electrons.com/source/drivers/mtd/nand/sunxi_nand.c#L219

Jan Glauber

author

2016-09-23 12:26 UTC #2 lore raw

Quoted 34 lines · Boris Brezillon

Hi Jan,
Quoted 22 lines · On Fri, 23 Sep 2016 13:29:44 +0200 Jan Glauber…
Hi all,
I'm working on a driver for the NAND controller on Cavium's ThunderX.
So far I implemented the low-level functions for using the controller to access a NAND chip. I can read the ONFI ID and parameter page with that.
Now I wanted to use nand_scan() instead of manually reading the chip parameters, but it fails with "No NAND device found".
The hardware I'm using has one NAND device wired as chip 1 (the NAND controller support chips 0..7).
The reason for the failure seems to be that nand_get_flash_type() returns an error before all the chips are scanned. What I don't understand is in that function chip 0 is selected before the loop that would scan all chips:
        /* Select the device */
        chip->select_chip(mtd, 0);
Quoted 6 lines
My select_chip() stores the chip number (in that case 0) and uses that for subsequent commands to the controller. Since there is no chip 0 the read returns nothing and nand_scan() fails.
Probably I'm missing something, would be great if someone could help me...

Quoted 6 lines

Actually, the chip parameter passed to ->select_chip() is not the CS-id from the NAND controller PoV, but the one from the NAND chip PoV.
You have to store an association table between chip⁻CS and controller-CS somewhere in your NAND controller private struct (a struct inheriting from nand_control_hw).

Thanks Boris. So far I only knew about controller-CS, so that confused me. So I'll have:

- one nand_hw_control
- up to 8 chips (if present)

Then I probably don't need the chip->select_chip() at all.

Quoted 6 lines

And remember that nand_scan_ident() is supposed to detect a single NAND chip, not all the chips connected to your controller (the multi-CS logic is here to handle multi-dies NANDs, not the case where you have multiple NAND chips connected to the same controller).
You can have a look at the sunxi_nand [1] driver if you want an example.

That's a much better example then what I've been looking at so far...

Thanks again,
Jan

Quoted 5 lines

Regards,
Boris
[1]http://lxr.free-electrons.com/source/drivers/mtd/nand/sunxi_nand.c#L219