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Re: [Qemu-devel] [PATCH v2] pflash_cfi01: fix per device sector length i

From: David Engraf
Subject: Re: [Qemu-devel] [PATCH v2] pflash_cfi01: fix per device sector length in CFI table
Date: Tue, 17 Jan 2017 17:48:11 +0100

Am 16.01.2017 um 11:26 schrieb Dr. David Alan Gilbert:
* Andrew Jones (address@hidden) wrote:
On Thu, Jan 12, 2017 at 10:42:41AM +0000, Peter Maydell wrote:
On 12 January 2017 at 10:35, David Engraf <address@hidden> wrote:
The CFI entry for sector length must be set to sector length per device.
This is important for boards using multiple devices like the ARM Vexpress
board (width = 4, device-width = 2).

Linux and u-boots calculate the size ratio by dividing both values:

size_ratio = info->portwidth / info->chipwidth;

After that the sector length will be multiplied by the size_ratio, thus the
CFI entry for sector length is doubled. When Linux or u-boot send a sector
erase, they expect to erase the doubled sector length, but QEMU only erases
the board specified sector length.

This patch fixes the sector length in the CFI table to match the length per
device, equal to blocks_per_device.

Thanks for the patch. I haven't checked against the pflash spec yet,
but this looks like it's probably the right thing.

The only two machines which use a setup with multiple devices (ie
which specify device_width to the pflash_cfi01) are vexpress and virt.
For all other machines this patch leaves the behaviour unchanged.

Q: do we need to have some kind of nasty hack so that pre-2.9 virt
still gets the old broken values in the CFI table, for version and
migration compatibility? Ccing Drew for an opinion...

I'm pretty sure we need the nasty hack, but I'm also Ccing David for
his opinion.

Hmm I don't understand enough about pflash to understand the change here;
but generally if you need to keep something unchanged for older
machine types, add a property and then set that property in
the compatibility macros.

See include/hw/compat.h, I think you'd add the entry to HW_COMPAT_2_8
and follow a simple example like  old_msi_addr on intel-hda.c,
that should get picked up by aarch, x86, ppc etc versioned machine types.

This is a new version of the previous patch including the HW_COMPAT entry.

After further tests with u-boot and Linux, I found another problem with the blocks per device and write block size. Blocks per device must not be divided with the number of devices because the resulting device size would not match the overall size. However write block size must be modified depending on the number of devices because the entry is per device and when u-boot writes into the flash it calculates the write size by using the CFI entry (write size per device) multiplied by the number of chips.

Here is a configuration example of the vexpress board:

sector-length = 256K
width = 4
device-width = 2

The code will fill the CFI entry with the following entries
num-blocks = 256
sector-length = 128K
writeblock_size = 2048

This results in two chips, each with 256 * 128K = 32M device size and a write block size of 2048.

A sector erase will be send to both chips, thus 256K must be erased. When u-boot sends a block write command, it will write 4096 bytes data at once (2048 per device).

I did not modify the CFI entry for write block size. Instead I kept the hard coded value of 2048 in the CFI table and fixed the internal entry for writeblock_size.

Best regards
- David

Signed-off-by: David Engraf <address@hidden>

Attachment: fix_pflash_sector_len_v2.patch
Description: Text Data

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