[PATCH] i2c: mediatek: fix WRRD for SoCs without auto_restart option

[Roman Vivchar]

Hi AngeloGioacchino,

On Thursday, July 9th, 2026 at 2:46 PM, AngeloGioacchino Del Regno <angelogioacchino.delregno at collabora.com> wrote:

> On 6/23/26 23:40, Roman Vivchar via B4 Relay wrote:
> > From: Roman Vivchar <rva333 at protonmail.com>
> >
> > MediaTek mt65xx family SoCs have no auto restart, however, they still
> > support the WRRD mode in the hardware. Because auto_restart is set to 0,
> > the WRRD mode will be never enabled, leading to read errors.
> >
> > Fix this by removing auto_restart check from the WRRD enable path.
> >
> 
> Are you sure that MT6577 and MT6589 do support WRRD?

Yes, I have checked their downstream kernels[1][2] and they both mention
WRRD.

We also tested mt6589 (privately) and the i2c was working. To be fair,
it had some other fixes, but at worst this patch is no-op.

mt6577 is a tough one... I don't think there's any recent kernel with
it. I plan to make it work with upstream, but that's a TODO. Either way,
vendor code has WRRD support.

> If you're not 100% sure, or you want to be careful (which I would, in this case),
> please add a `unsigned char wrrd_supported:1` to struct mtk_i2c_compatible, set
> it to `1` on *all* of the SoCs that support auto_restart (as that's effectively
> a different feature - it just happens that all the ones supporting this also do
> support that, up until today), and add a new one for your MT6572, declaring no
> auto_restart but wrrd_supported.
> 
> That would make me sure that you're not breaking anything, and would guarantee
> you a R-b.
>

As far as I know, there's no SoC without both auto restart and WRRD.
Adding wrrd_supported that always equals to true sounds redundant to
me.

Let me know if you still prefer having separate flag for the WRRD.

> Cheers,
> Angelo
> 

[1]: https://github.com/GoldRenard/lenovo_A390_mt6577_uboot_kernel/blob/38ea59263984e26c0dd8e5891b22a35f61e60ed5/mediatek/platform/mt6577/kernel/drivers/i2c/i2c.c#L963-L975
[2]: https://github.com/bq/aquaris-5/blob/bc1d0d0e35c969670e2d869001be944ad0c9c5e5/mediatek/platform/mt6589/kernel/drivers/i2c/i2c.c#L728

Best regards,
Roman