Re: [Bug 1905297] [NEW] Zynq7000 UART clock reset initialization

[Philippe Mathieu-Daudé]

Hi Michael,

On 11/23/20 5:41 PM, Michael Peter wrote:
> Public bug reported:
> 
> Hello,
> 
> we have come across a strange behavior in the Zynq7000 model of Qemu
> that seems to have been  introduced between 5.0.0 and 5.1.0.
> 
> 
> The reset values of the SLCR register, in particular those for UART_CLK_CTRL, 
> are such that
> the UARTs should find functional clocks. Up to 5.0.0 this was also the 
> behavior that was
> implemented in QEMU.
> 
> Starting in 5.1.0, we found that - despite correct reset values [1] - the 
> UARTs are non-functional
> upon reset. Some investigation revealed that the cause for that is that the 
> corresponding
> clocks are not properly initialized.
> 
> Between 5.0.0 and 5.1.0, there are three commits  that touch the Zynq
> UART clocks [2]. The last of them [3] triggers the faulty behavior.
> 
> Attached is a patch that applies 5.2.0-rc2 and yields a functional UART. We 
> surmise that the
> underlying device release issue runs much deeper, so it is only meant to 
> identify the issue.
> 
> 
> [1] hw/misc/zynq_slcr.c
>       static void zynq_slcr_reset_init(Object *obj, ResetType type)
>        s->regs[R_UART_CLK_CTRL]  = 0x00003F03;
> [2] 38867cb7ec90..5b49a34c6800
> [3] commit 5b49a34c6800d0cb917f959d8e75e5775f0fac3f (refs/bisect/bad)
>       Author: Damien Hedde <damien.hedde@greensocs.com>
>       Date:   Mon Apr 6 15:52:50 2020 +0200
> 
> ** Affects: qemu
>      Importance: Undecided
>          Status: New
> 
> ** Patch added: "0001-Initialize-Zynq7000-UART-clocks-on-reset.patch"
>    
> https://bugs.launchpad.net/bugs/1905297/+attachment/5437267/+files/0001-Initialize-Zynq7000-UART-clocks-on-reset.patch
> 

Can you post your patch to the mailing list
please? See:
https://wiki.qemu.org/Contribute/SubmitAPatch#Do_not_send_as_an_attachment

Note, you must sign your patch with a Signed-off-by:
line, see:
https://wiki.qemu.org/Contribute/SubmitAPatch#Patch_emails_must_include_a_Signed-off-by:_line

Regards,

Phil.