Re: [Qemu-devel] [PULL 27/27] hw/block/pflash_cfi02: Reduce I/O accesses to 16-bit

[Philippe Mathieu-Daudé]

On 7/3/19 5:52 PM, Stephen Checkoway wrote:
> 
> 
>> On Jul 1, 2019, at 20:59, Philippe Mathieu-Daudé <address@hidden> wrote:
>>
>> Parallel NOR flashes are limited to 16-bit bus accesses.
> 
> I don't think this is correct. The CFI spec defines an x32 interface for 
> parallel NOR. CFI addresses 0x28 and 0x29 specify the interface and value 3 
> is x32 and value 5 is x16/x32.
>
> Here's an example of an x32 device 
> <https://www.mouser.com/datasheet/2/100/002-00948_29CD032J_S29CD016J_S29CL032J_S29CL016J_3-1316792.pdf>.

OK, I was not aware of these.

QEMU never CFI-announced itself as x32 capable:

    /* Flash device interface (8 & 16 bits) */
    pfl->cfi_table[0x28] = 0x02;
    pfl->cfi_table[0x29] = 0x00;

So while the commit description is incorrect, the code is safe with the
current device model.

I am not comfortable keeping untested 32-bit mode.
Were you using it?

Regards,

Phil.

> Cheers,
> 
> Steve
> 
>> Remove the 32-bit dead code.
>>
>> Reviewed-by: Alistair Francis <address@hidden>
>> Message-Id: <address@hidden>
>> Signed-off-by: Philippe Mathieu-Daudé <address@hidden>
>> ---
>> hw/block/pflash_cfi02.c | 5 +----
>> 1 file changed, 1 insertion(+), 4 deletions(-)
>>
>> diff --git a/hw/block/pflash_cfi02.c b/hw/block/pflash_cfi02.c
>> index 83084b9d72..5392290c72 100644
>> --- a/hw/block/pflash_cfi02.c
>> +++ b/hw/block/pflash_cfi02.c
>> @@ -317,8 +317,6 @@ static uint64_t pflash_read(void *opaque, hwaddr offset, 
>> unsigned int width)
>>     boff = offset & 0xFF;
>>     if (pfl->width == 2) {
>>         boff = boff >> 1;
>> -    } else if (pfl->width == 4) {
>> -        boff = boff >> 2;
>>     }
>>     switch (pfl->cmd) {
>>     default:
>> @@ -449,8 +447,6 @@ static void pflash_write(void *opaque, hwaddr offset, 
>> uint64_t value,
>>     boff = offset;
>>     if (pfl->width == 2) {
>>         boff = boff >> 1;
>> -    } else if (pfl->width == 4) {
>> -        boff = boff >> 2;
>>     }
>>     /* Only the least-significant 11 bits are used in most cases. */
>>     boff &= 0x7FF;
>> @@ -710,6 +706,7 @@ static void pflash_write(void *opaque, hwaddr offset, 
>> uint64_t value,
>> static const MemoryRegionOps pflash_cfi02_ops = {
>>     .read = pflash_read,
>>     .write = pflash_write,
>> +    .impl.max_access_size = 2,
>>     .valid.min_access_size = 1,
>>     .valid.max_access_size = 4,
>>     .endianness = DEVICE_NATIVE_ENDIAN,
>> -- 
>> 2.20.1
>>
>