On Fri, Mar 8, 2019 at 7:29 PM Wolfram Sang <wsa@xxxxxxxxxxxxx> wrote: > > On Fri, Feb 22, 2019 at 02:04:11PM +0800, Hsin-Yi Wang wrote: > > Thanks for the solution. > > Previously we were testing if the driver can handle zero-length > > transfer, but it turns out it will timeout. (Also checked this from > > mtk's datasheet) > > Adding original owner qii.wang to verify that. We'll apply this after > > verification. > > I just checked this issue again and concluded that both are reasonable, > the suggestion from me below with the adapter quirk AND your original > patch setting the threshold to 1. With my suggestion the core will > prevent 0-length messages. But still, we should set the threshold to 1 > because 0 is a value the HW is not capable of. > I think quirk might be better, since mediatek said they might have some ICs that can handle zero-length transfer in the future, so flags might be more clear if they want to restore functionality. > > > > On Sat, Feb 16, 2019 at 12:36 AM Wolfram Sang <wsa@xxxxxxxxxxxxx> wrote: > > > > > > > > > >> > Ok, I can add a check in another patch. Should we return NULL pointer > > > >> > if msg->len is 0 or print out some warnings? Thanks. > > > >> > > > >> No warning, msg->len == 0 is a valid setting. But interesting question: > > > >> I was about to say NULL, but your driver would assume ENOMEM there and > > > >> discard the message which is also not correct since msg->len == 0 is a > > > >> valid setting. So, should we just return msg->buf then? Will this work > > > >> with your driver? Can it handle zero-length transfers? > > > > > > > > dma_map_single(i2c->dev, msg->buf , msgs->len, DMA_TO_DEVICE); breaks > > > > kernel if msgs->len is 0, so I think it doesn't handle zero-length transfer. > > > > > > Please don't drop the lists. > > > > > > Then, the correct solution is to forbid those transfer with this > > > controller. Check I2C_AQ_NO_ZERO_LEN. Also, update the functionality > > > like this .. (I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK). > > >
